Single player is pretty poor, but I had a good time with multiplayer. Of course, that was summer of '06 when pickings were pretty slim on the 360.
It's just one of those games that was great at the time and hasn't aged well. Halo 3, Gears 1 and 2, Call of Duty and Battlefield all blow it out of the water. Normally I'd say single player is worth it for that price, but the story was just insultingly bad compared to the first Perfect Dark. I can't even recommend this game to big fans at this point in time.