I thought I was off to a good start when I put COWTIPPING (1A: Rural activity in an urban legend) in immediately (Just one of the many benefits of going to college in Wisconsin.), but then I tried "byob" for 11A: Acronym in casual dining (IHOP) (I wasn't thinking that casual!) ... it wasn't right, of course, but it does demonstrate nicely what this puzzle was like for me. I felt good, so I was putting in answers very quickly, sometimes with no backup at all, and sometimes they panned out, as with OPART (30A: Looking at it for a long time might make your head hurt) and PLAYBOYMAGAZINE (50A: Source of a controversial 1976 Jimmy Carter interview), and sometimes they didn't, as with "color" for 23A: "The breath of art," per Frank Lloyd Wright (SPACE) (a much better answer), and "hash" for 46A: ____ marks (SKID) (eww!).
Anyway, I loved it. There's just so much great, interesting, unusual fill in here. To start with, 1A gets an A. TRANSOMS (34D: Architectural crosspieces) is nice, BARQS (29D: Dad's rival) is delicious, JUICY (31D: Like some details) is fun, and FBOMB (37D: Impolite thing to drop) is fan-effing-tastic! The grid looks great with its expansive NW and SE corners and the wide swath running up through the middle, and there's very little to complain about.
Loved the cluing, loved the fill, loved the grid - loved it.