While I do predict Left 4 dead will be quite awesome, it's not out on shelfs or on his list.
For your moneys worth:
-Fallout will give you upwards of 100 hours of play if you let it, but if you are not a fan of action/RPG style games, then you may not enjoy it as much.
-I have only played gears for a few minutes but I can say that if you liked the first you will love the sequel, it's better in so many ways.
-Dead space is the third choice, not because it's bad, but because the campaign only took me 11hrs to beat, and in a week I had gotten all of the achievements, so unless you stumble upon 60 more dollars I would go with the first 2.
Now Im off to go do something productive