Wow, I don't remember liking a puzzle this much for quite a while. The theme of CASEY (16A: Man trying to clarify the spelling of his name in…) to QRCIU (66A: What the listener might think 16-Across's name is?) is hilarious, and even though, once you got it, the "ASIN" part of the clues could be filled in without thinking, I still laughed every time. And really, we didn't have much left to fill in by the time we figured it out.
And even with all the exacting, symmetrical theme, the fill was actually very good. In fact, there was so much fun clueing (52A: College softball? (EASYA) & 27D: Support staff (CANE)), interesting factoids (4D: Elasticity symbol, in economics (EPSILON) & 5A: Like more than a third of U.S. immigrants nowadays (ASIAN)), and modern stuff (KIMYE (32D: Celebrity couple portmanteau) & YOLO (58D: Modern acronym suggesting "seize the day")), that a slightly larger-than-normal 16x15 grid was needed to fit it all!
As I look through this, it is taking some effort to both not call out every other clue as one I like, and to find any clue or answer that I don't like. It's just that good. Take the clue pair 43A: Fair (EXPO) and 48A: Not fair (RAINY) - neither is what I first expected! 6D: General reception? (SALUTE), brilliant. 5D: Tree in a giraffe's diet (ACACIA), interesting. 35D: Part of a black cloud (GNAT), nice clue. 38D: It's always underfoot (SOLE) (tried "soil" first), tricky! A little French, a little Italian, a little Spanish, a little Latin… it's got everything. I loved it, and so did the MISSUS.
A thoroughly enjoyable Thursday.