Halo has a shorter campaign. If you don't want mp, then don't get halo. Half Life has the two episodes, so in total it's around 50 hours. However, I find Crysis has the best gameplay, and you can play any way you want. There are different suit abilities that you can use and customizable weapons. And there are WAY more weapons in that game than Half Life 2. Half Life 2 has like, 10 weapons. Crysis has loads of weapons! If you want something different, then get Crysis. If you want something long, get the orange box. Portal is also pretty good.

I'm gonna play both, one reason is the stroy, the other is split screen on RFOM. My friends come over, and I don't have any split screen games, so this is a must buy for me. I wanna trade in a couple of games anyway, and there like, $20 each. You might as well, or you can play FOM, then trade it in for R2.