Probably get slated for saying this but either Call of Duty 4: Modern Warfare or Call of Duty: World at War. Much better than the later ones. I think WAW has taken up about 11 days of my life altogether with 4 another 7 days. Also loved Assasins Creed Brotherhood and Halo 4 especially for its graphics.
I second Fallout 3 - it was incredible in every way: concept, atmosphere, soundtrack, graphics, storyline... wonderful. Also, Red Dead was good though I got bored with it. However, it provided my favourite gaming moment ever when crossing the river to Mexico for the first time. Worth it for that alone
Oh, and BF3. Had a K/D of 2.2 before I sold off the console (Xbox Live Gold is a complete rip off - it must have cost me £200 over the life of the machine).
I agree completely on both counts, Red or Dead just lacked something. I'm going to have to go for Skyrim as my all time fav though. Fallout 4 is going to be great.
Love The Orange Box, so glad Half-Life came to console. I would vote it best value for money, 5 games in one. Love fallout 3 and New vegas but I'm playing Skyrim now and it's simply blown every game i've ever played clean out of the water and I've barely scratched the surface. Skyrim for me! I find the CoD's far too short and restrictive. Special shoutouts to Dead Rising, Bio Shock and the MotorStorm. All very special games in their own quirky way.