Be honest though, was it the words coming out of Will Smith's mouth* or Jones's constant, unfettered "I cannot believe this guy won't shut up" expression that made those scenes?
It's both. There's a reason the straight-man role is so prevalent in comedy. John Cleese may be the first person you think of when you think of all the funniest Python bits, but try picturing them without Graham Chapman. (Hell, swap another goofy character in -- say Eric Idle in one of the Chapman parts opposite Cleese. Say the Dead Parrot Sketch was Cleese and Idle instead of Cleese and Chapman. Loses a bit of its shine, doesn't it?)
Anyhow, yeah, there are much better movies right now (thinking maybe Hugo this weekend, and wondering if The Artist is playing anywhere), but I'll probably catch MIB3 eventually. Pity about Jones sidelining himself, but Brolin's a good replacement and hey, Jemaine Clement as the villain.