SOF2 is a great game. Well multiplayer wise. I never even made it throught the first single player mission because I like the multiplayer so much. I'd say if you like single player games pass on it, but if you like multiplayer games pick up a copy.
The best way I can summarize the game is it is like Counter-Strike (minus the cash for weapons), Rogue Spear, and Delta Force all rolled into one. It has CTF, TDM, DM and INF (or counter-strike style) gameplay and has great indoor and outdoor maps. It also has random map generation for some of the outdoor maps. One drawback is that there is not a wide variety of weapons, but what is there is fairly realistic. Overall graphics are outstanding on my P4 Radeon 8500.
I have hardly played MOHAA since buying SOF2 if that is a good indicator. I still like MOHAA, but it seems to get really laggy even on DSL.
Something to consider is America's Army is free and although I was only able to play a few minutes on a server due to all the problems they have had it does look like it may give a similar game play for free. I can't stand having to use Gamespy though so I hope the in game browser is working soon for AA.
SOF2 has a great in game server browser FYI.