I would say ether left 4 dead or left 4 dead 2. It is an awesome game and I recommend buying them.
yes
no
The Xbox 360 has the best library of multiplayer action games.
If you get call of duty black ops there is a zombie mode and you can play it online.(There are other call of duty's with zombie modes.)
All games have access to Xbox Live; it's just a matter of the multiplayer, and Assassin's Creed 2 does not have multiplayer.
dead island is my favorite.
if you want to play multiplayer on the xbox 360 you can with and without connecting to xbox live. some games you have to connect to xbox live and some you don't. when you buy a game look at the back of it and it should tell you.
left for dead 2
It is todally your decision, they both have a good games If you want Story Games get a PS5 If you want Multiplayer games get XSX
if it can play on the Xbox 360 then it should be able to go online
Yes http://www.xbox.com/en-GB/games/backwardcompatibilitygameslist.htm
No you can't the game is only for xbox indie games.