By far the game I've played the most on Xbox Live has been Gears of War 2.  From a pure enjoyment stand point Gears 2 has given me more for my money than any other game.  What seems to be an issue with Gears of War 2 is the fairness of play online.  I've heard the stories about how over powered the shotgun is for the host.  I honestly never believed it until it was proven to me.

I play a lot of online with friends and for the most part I'm always the host.  We decided to give the host spot to another player after he kept complaining about the timing and physics in the game.  It was ugly, he was a shot gun whore and he killed us with ease.  It wasn't even close except for a couple maps.  Honestly I felt disenfranchised with the game because it seems to give an undue advantage to the server.  We ended up playing some Halo 3 for a while because that game is at least fair online.

We have moved back to playing Gears 2 but I still feel the game needs to be balanced out better.  It's no fun being totally dominated in a game.  No one keeps coming back to get their teeth kicked in every week.  It's really unfortunate because I prefer the action and maps in Gears over other online shooters.  Thankfully there are other game modes to play that I do enjoy.  I'm playing a lot more Horde mode now that I can gain experience points for each round. 

Epic has been tweaking the online experience of Gears of War 2 ever since it rolled out.  There is obviously a nice sized community out there.  In online matches you never really know who is the server so you just see people ignoring the lancer for the shotgun.  Hopefully Epic will improve their game to the point where all weapons are fair in multiplayer matches and no one has an undue advantage.  This is probably why games like Call of Duty 4 and Halo 3 have become more popular online.  In Gears of War 3 hopefully we'll see a balanced, fair multiplayer game.