What a fun theme! I was definitely confused to begin with. I put "agar" in a 1A: Cel material ([ACE]TATE), misreading the first word as "cell". Even then, the answer I chose is odd. I recognized it was wrong immediately because of 1D: "L'chaim!" (TOLIFE). Ah, Fiddler On The Roof.
I worked my way off of that answer into the SW corner. ARIETTA and scattered answers in the bottom got me RELIESON. I noted the "-" clue at 56D, and then got the revealer at 52A: Hidden advantage that this puzzle employs four times? ([ACE]INTHEHOLE). Very clever idea, using the black square as the hole, implying "ace". And this answer is the only one where it actually means "Ace".
My favorites are ADJ[ACE]NTTO and CRET[ACE]OUS, not least because they have to be symmetric and thus the same length and (inverse) pattern. LIBER[ACE] and VERS[ACE] are fine, although they both rely on the Italian endings. Also very nice is AMAZINGGR[ACE].
What's really nice about this puzzle is that because the theme material is primarily on the outer edges, the rest of the puzzle plays like a wide open themeless. Two excellent 10-letter non-theme answers are BLACKSHEEP and JULESVERNE. I love the piece of trivia for the latter. Who knew? I'd have guessed J.K. Rowling nowadays...
There are some odd entries: IIN is one of the stranger partials I've come across. INDC looks mighty peculiar, but it was pretty straightforward from the clue. 49D would be better clued in another way, even if it is topical nowadays.