This one was all over the place and, unless we're missing something, themeless. It had odd variants like HOODOO (22D: Jinx) instead of the more common voodoo, and AWMAN (9D: "This is the worst!") instead of the all-to-common adman. And we've got UNAPT (40D: Not fitting) (don't we wish!), and STET and ESTE... no "eel," but then, you can't have everything.
On the plus side, we could find some enjoyment in the utter absurdity of UCANTTOUCHTHIS (51A: Signature song for MC Hammer) crossing OHOLYNIGHT (31D: Carol with the words "hear the angel voices"). It's May, in 2013, right? And not December, 1990?
We liked NEATNIKS (39D: Tidy types), SLOSH (65A: Wade noisily), and MEME (18A: Viral phenomenon), and the puzzle did require a little more effort than most Mondays (we actually got to pass it back and forth once or twice!), so on balance, it comes out slightly ahead.
p.s. We did miss the theme. The answers for 20A, 3D, 38A, 31D, and 51A start with the five vowels.
p.p.s. I almost liked it better before learning that.