COD: black ops is not a bad game, but I don't think it needs to exist. COD 2 was an improvement of prior CODs, MW was better than COD2, and MW2 was better than MW. But is black ops better than MW2?    
 
The roller coaster ride of crazy shit happening was perfected in MW and MW2 and nothing is improved in the newest COD game.  The story is arguably better in black ops (minus Worthington's voice acting) but the ridiculous (and often nonsensical) story is not why anyone plays COD games (at least as far as I can tell). Also, I died repeatedly when the game did a poor job of communicating how to win a certain scenario, which I don't remember happening in other COD games.   The co-op zombies mode is inferior to the spec-ops mode of MW2 and the multilayer is basically unchanged from MW2, though there have been a few tweeks and the maps are the large warrens that Treyarch makes. They seem to have toned down the killstreaks, which is an improvement, but otherwise the multiplayer is no better or worse than last years COD game.  
 
The only other think worth noting is the "wager" mode, which is interesting but not really anything new. Other games where you can rank up and down (like halo 2 and 3) are essentially wager modes under another name. In those types of games you are wagering your  rank, if you win you go up in rank and if you lose go down in rank. And in FFA halo 2 and 3 I think the top three were considered winner and the rest losers.  What might be more interesting is if you played several short rounds of games (team based or otherwise) where you can bluff (play intentionally bad in the open round where you bet little) then bet more after you have lulled your opponents into a false sense of security. Or perhaps you could bet about what types of weapons you will beat the other teams with.  
 
Black Ops is an OK game and maybe I'm just burnt out on the franchise, but why does it exist?