The Space Marine Strikeforce is the replacement for the Battleforce. However, it's focused on being a kind of "starter army" box built around a theme of some kind.Every army will get one (possibly more) eventually that will be named after something relevant to that army (example: Wraithhost for Eldar).
General Information:
240 Points for 3 Centurions with Grav-Cannons/Grav-Amps and Hurricane Bolters
Assault Centurions have Move Through Cover
Codex: Space Marines is largely in line with Codex: Dark Angels points wise.
176 Pages in their copy of the codex (same as rumored)
Hunter has "Savant-Lock". When shooting at a flyer you put a marker on it for each miss. The markers stay on the flyer until it leaves the table or is destroyed. At the beginning of every friendly shooting phase you roll for those markers. On a 5 or a 6 that missle hits.
Artwork is nice, and book is Space Marines more in a general form. More updated fluff, not just the rehashed fluff.
Some of the classic Black and White was colored, but a lot of new art too.
Book is in sections for each founding chapter (plus the Black Templars)) and a large number of the Successor Chapters to help players know who should be using what rules.
Salamanders don't really have any successor chapters because their chapter had suffered a large number of casualties so they have a larger number of Marines in their chapter.
"Equivalent to Forge World background" in terms of fluff.
Forgeworld fluff included in the codex.

Warlord Traits (Only One Chart for the Codex):
1. Angel of Death - Warlord and his unit have the Fear special rule.
2. Imperium Sword - One use only. Declare that your Warlord is using this at the start of one of your assualt phases. The Warlord and his unit have the Furious Charge special rule until the end of the turn.
3. Storm of Fire - One use only. Declare that your Warlord is using this at the start of one of your shooting phases. For the duration of that phase a single friendly unit from Codex: Space Marines within 12" of the Warlord may re-roll any failed to-hit rolls.
4. Rites of War - When taking morale tests friendly units from Codex: Space Marines within 12" of the Warlord use his characteristic instead of their own.
5. Iron Resolve - When determining your assault results add +1 to your total if the Warlord is locked in that combat.
6. Champion of Humanity - If your Warlord causes the enemy Warlord to be removed from play in a challenge he scores D3 extra victory points in addition in the usual amount of points given for slaying the enemy Warlord in this scenario. Note that killing the enemy Warlord in a sweeping advance does not reward these extra victory points.

Chapter Tactics
Successor Chapters - You use whatever chapter tactics of your parent chapter. The ONLY Exception is the Black Templar.
Homebrew - You can pick any tactic you want and use the Special Characters of that chapter. Those characters have to use the same Chapter Tactics as the same Chapter their from.
Allies - "A Space Marine Detachment that has one set of Chapter Tactics MAY ally with another Space Marine Detachment with a different set of Chapter Tactics, Ultramarines and Raven Guard for example. For purposes of the Allies rules these allies are treated as being from two different codexes and are treated as Battle Brothers. Note that you may field models from two different chapters that have the same Chapter Tactics, such as Ultramariens and Praetors of Orpheus in the same detachment. These chapters are so closely affiliated that they count as a single army on the battlefield."
COUNT AS: If you want to use Vulkan in a Ultramarines army you have to play use the Salamander Chapter Tactics. So you CAN do "count-as" but you lock yourself into their Chapter Tactics. In short, Special Characters are locked to their specific Chapter Tactics.

Ultramarines - Combat Doctrine: This detachment can utilize each of the following combat doctrines once per game. To do so at the start of your turn you state which combat doctrine you wish to use, if any, until the start of your next turn. You can only use one combat doctrine per turn.
Tactical: Units in this detachment re-roll ones while shooting, unless they're tactical marines and they re-roll all failed to hit rolls in the shooting phase.
Assault: Units in this detachment can re-roll their charge range. Assault squads, bikes, or attack bikes instead have the fleet rule.
Devastator: Units in this detachment may re-rolls to-hit on snap shots, including overwatch shots, in addition models in this detachment's Devastator squads have the relentless unless they disembarked from a transport in their movement phase.

White Scars -
Born in the Saddle: Models in this detachment with the Bike Unit Type automatically pass Dangerous Terrain tests, and recieve a +1 to their Jink Cover Saves. In addition add 1 to their Strength when resolving their Hammer of Wrath hits.
Fight on the Move: Models in this Detachment have the Hit and Run Special Rule. Note that this does not include models in Terminator Armor, Devastator Centurions or Assault Centurions.

Imperial Fists -
Bolter Drill: Models in this detachment may re-roll all to-hit rolls of 1 made with a bolt pistol, boltgun, stormbolter, heavy bolters, or combi-weapons that are firing as boltguns. This rule does not apply to Helfire, Kraken, Vengence or Dragonfire rounds.
Siegemasters: Models in this detachment in Devastator squads and Centurion Devastator squads have the Tank Hunter special rule and add +1 when rolling on the building damage table.

Black Templars -
Accept Any Challenges, No Matter the Odds: When engaged in a challenge, Black Templar Characters reroll all failed to-hit rolls, and have the Rending Special Rule.
Crusaders: Black Templars have the Crusader and Adamantium Will Special Rules. In addition Black Templars have access to a special unit called a Crusader Squad.

Iron Hands -
The Flesh is Weak: Models in this detachment have the Feel no Pain on a 6+ Special Rule. Note that if they benefit from more than one instance of Feel no Pain they use the best version available.
Machine Empathy: All vehicles and characters in this detachment have the It Will Not Die special rule even though vehicles do not have Chapter Tactic special rules. Furthermore, Techmarines and Masters of the Forge in this detachment add +1 to their Blessing of the Omnissiah rolls.

Salamanders -
Flamecraft: Models in this detachment can re-roll their saving throws against wounds caused by flamer weapons as defined by the Warhammer 40,000 rulebook. Furthermore, flame weapons used by models in this detachment re-roll failed to-wound rolls and armor penetration rolls that don't cause a glancing or a penetrating hit.
Master Artisan: During the army selection each character in this detachment may upgrade on of his weapons, even one they have purchased as an upgrade, to have the Mastercrafted Special Rule at no additional cost.

Raven Guard -
Strike from the Shadows: Models in this detachment have the Scout Special Rule. In addition, on the first game turn, models in this detachment have the Stealth Special Rule. Note that units that include models with the Bulky or Very Bulky Special Rules do not benefit from either rule.
Wings of Deliverance: Jump Infantry Models in this detachment may use their Jump Packs in both the movement and assault phases of the same turn. Futhermore, they must re-roll all failed to-wound rolls caused by their Hammer of Wrath hits.

Special Characters:
Marneus Calgar:
+25 Points
Artificer Armor standard (2+)
God of War: May use a single Combat Doctrine twice per game
Titanic Might: Re-rolls all armor penetrating hits in close combat. He may reroll glancing hits to attempt to get a penetrating hit. Must accept the second roll even if it is worse than the first.
Terminator Armor is 10 points and doesn't prevent sweeping advances.Warlord Trait: Rolls 3 times on the Warlord Table, rerolling doubles, and chooses a single Warlord Trait.

Captain Cato Sicarius:
-15 points
Surprise Attack: +1 to Reserve Rolls
Weapons still the same
Battle-forged Heros: Pick a Tactical Squad and they gain Counter-Attack, Infiltrate or Scout.
May still use the Coup-de-Grace with his sword.
Lost Rites of Battle
Warlord Trait: Imperium Sword

Tigirius:
-65 points
+1 Wound
Master Psyker: May re-roll any or all of his rolls to choose which powers he knows. He has access to all the powers.
ML3
Hood of Hellfire: Psychic Hood that allows you to re-roll failed psychic tests
Rod of Tigiruis: Same as before with the addition of Soulblaze
Gift of Prescience: If your army contains Tigirius you may choose to re-roll reserves and apply the result to units of the same attachement.
Warlord Trait: Storm of Fire

Cassius:
Zealot
All equipment the same
Warlord Trait: Angel of Death

Telion:
Chapter Tactics: Ultramarines
Same points cost
Same rules

Sergeant Chronus:
-20 points
+1LD
His vehicle gains It Will not Die

Khan:
-35 points (bike is still 20 point upgrade)
Bike does D3 Hammer of Wrath hits
Furious Charge
If Khan is your warlord friendly models with the Chapter Tactics White Scars special rule that are bikes or have dedicated transports have the Scout special rule.
Khan makes all bike squads who are 5 bikes or more count as troop choices.
Warlord Trait: Champion of Humanity

Vulkan:
The Forgefather: If Vulkan is your warlord, all meltas, multi-meltas and combi-meltas in this detachment become twin-linked.
Lost Digital Weapons
No longer Master Crafts Thunderhammers
Warlord Trait: Iron Resolve

Shrike:
-10 points
Stealth
Before deploying Shrike can only join a Jump Infantry unit
Lost Fleet
Weapons stayed the same
Warlord Trait: Angel of Death

Lysander:
+30 Points
No more Bolter Defenses
Icon of Obstinancey: All models with the Imperial Fist Chapter Tactics re-roll failed morale and pinning checks
Same wargear
Warlord Trait: Champion of Humanity

Chapter Master Pedro Kantor:
+1 Attack
Oath of Rynn: If Chapter Master Kantor is your Warlord all models in Crimson Fist detachments have the Preferred Enemy (Orks) Special Rule. Furthermore, all such models within 12" of Kantor have +1 Attack while he lives. This bonus does not affector Kantor, and is not cimulative with the similar bonuses that the Chapter Banner gives.
Still has Hold the Line (Crimson Fist Sternguard Veterans are scoring)
Same Wargear and points
Warlord Trait: Iron Resolve

Helbrecht:
+5 points
+1 WS
Rites of Battle - Gone
Crusade of Wrath: Once per game, during the Assualt Phase, all models with the Black Templar Chapter Tactics gain Hatred and Fleet until the end of the phase.
Sword of the High Marshalls is the same
Legacy of Dorn (+D3 attack on the charge) same

Grimaldus:
-10 Points
-1 BS
+1 Wound
-1 Attack
It will Not Die (replaced "Only in Death Does Duty End")
Zealot
Relics of Hellsreach: Any Black Templar of a servitor in 6" gains a 6++ Invunerable save.
Unmatched Zeal: Black Templar models within of 6" of Chaplain of Grimaldus have the Zealot special rule.

Emperor's Champion:
Uses HQ Slot
+50 Points
2+/4++
Black Sword: AP2, Mastercrafted
Combat Stances: Smite the Unclean - +2 Strength, Black Sword is two-handed and unwieldy; Slay the Heretic - Rolls of 6s to wound are Instant Death
Bolt Pistol gives extra attack (unless using Smite the Unclean)

A Quick Summary of what Black Templars Gained and Lost (this list may not be complete):
Losses:
- No More Vows
- No More Marshalls or Castellans
- No More Terminator Command Squads
- No More Master of Sanctity/Reclessiarchy
- Sword Brethren are no longer units
- No More 2 Heavy Weapons in a 5 man Terminator Squad
- No More special rule upgrades (Tank Hunter, ect)
- No More Storm Shields on Assault Squads
- No More extra power weapons in bike squad
- No More Fearless in Close Combat
- No More Righteous Zeal
- Some Flavor
- Most Heavy Weapons +5 more
- No More Power of the Machine Spirt upgrade

Gains:
+ Chapter Master and Captains
+ Honor Guard
+ Regular Chaplains
+ Master of the Forge
+ Tactical Squads
+ Scout Squads
+ Land Speeder Storm
+ Vanguard
+ Sternguard
+ Ironclad Dreadnoughts
+ Centurions (Assault and Devastator)
+ Scout Bikes
+ Devastators
+ Whirlwinds
+ Hunter
+ Stalker
+ Land Raider Redeemer
+ Thunderfire Cannon
+ Crusader Squad keeps Land Raider Crusader as a Dedicated Transport
+ Initiates are 5 points cheaper (counting Frag and Krak Grenade upgrades)
+ Sword Brother option in Crusader Squad
+ Keep Initiate Power Weapon/Fist option
+ Neophyte leadership increased to Ld 8
+ Neophyte Shotguns S4
+ Crusader Squad keeps Pistol and Chainsword option
+ Crusader Squad Organization stays the same