It is an expansion which will give you multiplayer and additions to the single player campaigns including a new faction called the Sarranids (based on medieval Arabic traditions) and changes to AI and in game quests. The graphics are much better too.
I am in the beta and it is alot of fun. It is an expansion though, definately not standalone and I am sure it will work for Windows 7.
I am not sure what the collector edition gives you though
howcome it costs like £20? most of the improvements have already been developed on mods. all your paying for is the multiplayer and tbh i prefer it without. i think it was refreshing to play a game where the singleplayer was actually good enough to keep you interested for so long. probably gonna get the game anyway but i have a feeling that this will be a big step back. i hope im wrong...
I'm in the beta, I'm happy to pay £20 for the single player alone. :) People need to stop complaining about this, the same happened with L4D and L4D2. Both are still great games and the sequels are the price of an expansion pack.
And thanks for finally confirming about the collecters edition Roger, it had been annoying me for a while now.