Socom 2 is just better. Maybe I'm old school but I think the maps in Socom 2 are much better than anything offered in Socom 3. If Zipper were to include support for Socom 2 maps in Combined Assualt then I would consider buying it.
I agree with the others who bring up the fact that in Socom 3 you run for minutes just to get sniped and then wait for even longer for the round to end. I like the idea's they had for weapon upgrades but I feel like they should have built upon what they had in Socom 2 more.
What speaks the most to me is the amount of players still logging on the Socom 2 universe. See this post:
How many play every night?