Fable II is cool, not played Fallout or Rainbow Six Vegas (cba to buy it; didn't like the old ones very much) I hate Ghost Recon 2 (the original is good, though), love Halo 3 (2 is better though).
Have you played ODST? I played it on Saturday; I thought it was excellent. The campaign was good; bit too much story line for a Halo game. You'll love fighting hunters as a human. Firefight is excellent. Me and my friend couldn't get past 3 rounds (you fight 5 waves of covenant with limited ammo and 7 respawns (regardless of how many players there are); every 5th wave the game adds a Skull to make it harder and you get your ammo and respawns back. The third skull causes you only to regain your stamina when you melee an enemy; so it gets really hard. Add that to skulls 1 and 2 which causes the enemy to dodge grenades, needlers and rockets and throw more grenades... it's alot harder.
Luckily there's no Flood in this one; I hated them (the level Cortana in Halo 3 made me want to die; it was awesome looking around High Charity but it was really hard on Heroic and Legendary (on Legendary I failed to complete it; I couldn't get to the Artbiter with his flame thrower! I kept getting killed on the way back).
I wonder what Reach will be like... if this (
http://i38.tinypic.com/2r3ed8y.jpg ) is real; it should be good...
The only problem I have with Bungie is that they're going the same way as infinity ward -- the "red screen means hide" health system and including "perks" which is stupid.
Edit: they're over simplifying it, in short. I like the Halo attitude of "if you can't find <insert object here>; have fun looking at the effort we put into drawing the scenery," where you get at most a compass telling you where to do, vs. almost every other FPS' "Go over here, go there, now shoot for ten minutes." However Halo isn't a tactical game; which is good. You can play tactically though...
I hate infinity ward; you can tell they just want money... I think MW2 will be boring and I didn't buy MW for the same reason. I played the campaign at a friend's house and it was extremely dull. Multiplayer was too; it seems to "same old". Not saying Halo 3's is revolutionary; but it is fun to splatter with Mongooses (Mongeese?) and fly the Banshee around...