GETTING IN THE FINAL WORD
From the get-go this thing was looking good. UNJAM is a tricky answer for "1A: Free, as copies." CAUSE (18A: Gay rights, e.g.) is timely. NAGNAGNAG (23A: "Geez, get off my back already!" is fresh and fun, GLOBE (6A: Small world?) is cute… and we haven't even come to the theme yet, which is also excellent.
OK, so I liked it. What else… I immediately thought of "ephemeral" for 12D: Not here for long, but the real answer was an even better word (and the correct length!) - EVANESCENT. OPIUMDEN (36D: Smoke-filled establishment) was surprising. 102D: Off-color (BAWDY) and SPURT should make Huygens GOAPE. ECLECTIC (107A: Diverse), POUNCE (93A: Not let a big opportunity slip by, say), and TOWNDRUNK (114A: Stock character like Maybery's Otis) are all nice.
Sure, there's a nice crosswordese crossing at SSTS and STYE… I've never heard of PERL (93D: Physics Nobelist Martin, discoverer of the tauon) or ELMO (99A: Admiral Zumwalt), and I'd say AVE (20A: Hello from Hadrian) is more of a "goodbye" and "salve" is more of a "hello," but maybe I've just been using those wrong… and really, that small amount of barely questionable material is a small price to pay for a Sunday this good. Let's end on a couple more good ones - 89A: Guard at a gated community? (STPETER) and 121A: Age-old bug trap (AMBER). Good stuff!