The first list:
1) CoD4 is amazing on xbox live and is very fun for pretty much endless hours of fun, especially if you have friends who like to play this game online with you.
2) Halo 3 is the same as the the above, except it is more fun to play with friends(online and offline)
3) Gears of War 2 I haven't played much but it is a great game that has amazing graphics and has excellent xbox live gaming.
This list is great for xbox live. Without xbox live the Halo 3 and Gears of War 2 are fun, but CoD4 isnt.
The second list:
1) GTA4 is a really fun game but honestly can get boring after an hour or so of play. Many people I know just get bored and put in codes to do whatever they want for about 20 minutes then turn it off.
2) Sould Caliber IV is honestly a very bad game in comparison to the previous two, but overall is just ok without xbox live. With xbox live this game is terrible because even on the best internet connection you lag as much as your opponent on a bad internet connection does, making timing and the game as a whole unplayable.
3) Naruto Broken Bond is very boring in my opinion but my friend played it a lot and loved it for about a week, then never played it again.
This second list is more of a non-xbox live one, focusing more on the campaign really rather than online multiplayer(except for Soul Caliber IV which is terrible)
Obviously you can see a clear difference in the two here, one is great for xbox live and then other is not. Even without xbox live the campaigns on halo 3 and gears of war 2 are amazing, some will argue that GTA4's campaign is as well.