I thought Modern Warfare 3 was terrible, the only enjoyment I got out of that game was playing the co-op missions with a friend, and even that ranged from enjoyable to down right expletive inducing. It wasn't very well designed, a lot of areas felt like you just had to be lucky to get through them rather than skillful, what kind of game is that?
I hated the competitive multiplayer with a passion, the spawning was terrible and in my opinion they never bothered fixing it properly, the maps which shipped with the game were absolutely dire as well. A collection of very small mazes with 4 or 5 different entrances to each area, wow what great fun. For me the multiplayer was basically kill somebody, they respawn behind me, or in one of the ridiculous amounts of entrances to the area which I was in, they would kill me, I would respawn in one of the ridiculous amounts of entrances to the area they were in... repeat.
I thoroughly enjoyed Black Ops though, the campaign was enjoyable, I liked the story and the fact they got some big name voice actors, I also really enjoyed the multiplayer and I thought the maps were fantastic.