Another odd theme today, where the letter M ends the first word of a two-word phrase, and the letter R starts the second. The first three theme answers are all fine - BOTTOMROW (18A: 64-, 65- and 66-Across, in this puzzle) (Odd clue. And if you're not going to use the Oxford Comma, why put one after "66-Across?" That isn't really necessary, is it?), STEAMROLLER (20A: Heavy vehicle that smooths a road surface), and PALMREADING (55A: Means of fortunetelling). The last one - AMFMRADIO (58A: Audio feature that comes standard on cars) is a little less strong, because "AMFM" is an abbreviation, or at least it started out that way. I doubt many people could tell you off the top of their heads that it stands for "Amplitude Modulation/Frequency Modulation." I couldn't have, anyway. Good ol' Google.
And one last thing about the theme, when I got to the centrally-located revealer, I spent a lot of time wondering how I was going to spread "Jim" out across all those spaces. Silly me, though, because one doesn't mess around with Jim, and that clearly was not included.
So anyway, one thing I noticed as I solved this puzzle was a lot of things like MMLI (29A: The year 2051), OBI, ELS, OEO (24A: Antipoverty agcy.) (?), EDY, OZS, AMO, MRE, SRIS, and LMN (54A: K-O connector). That seemed like kind of a lot of short glue. And it starts off with a weird-ish partial ABANG (1A: Go out with ____). I probably would have liked this a little better if it were the final Across clue instead of the first, but as it is the first, I think I will give it a D.
On the bright side - and we always do prefer to "accentuate the positive" - I liked seeing fun words like GIZMO (5D: Thingamabob), FLUMMOX (39D: Discombobulate), and KABOOM (6D: Explosion sound). And the two-word, descending three-stack of TOREOPEN (11D: Ripped the wrapping off), INORBIT (12D: Circling the earth, say), and NOWAIT (13D: "Oh, hang on a minute!") was strong.
There's almost enough to "eliminate the negative," but not quite. Today, I'm afraid we're going to have to mess with MRINBETWEEN.