In my opinion, most everything about the game is brilliant, except the online multiplayer.
I personally loved the campaign, with all its set pieces and epic moments. Spec Ops is pretty good, not exactly my cup of tea though, with the insane difficulty. Splitscreen multiplayer is an absolute blast, it seems like the major flaws with killstreaks, overpowered weapons and tactics, etc. just disappear.
Online multiplayer, though, is terrible. People take it all way too seriously, abusing the most cheap tactics to get a high score, then bragging about it in the post-game lobby. People don't cooperate, they complain about everything, and it's just terrible.