Our themelesses are getting smoother and smoother, it feels like. I'm not surprised that Mr. Ezersky has produced such a lovely puzzle.
I broke in with that old standby, HYDROXYL. Ah, for the easy days of organic chemistry. It's great that it's crossed with 20A: An "A" in physics? (AMPERE). Humor only an UBERGEEK would love!
I disagree that a tuning fork has a YSHAPE. I don't know exactly how to describe what a tuning fork looks like. How about a picture?
It's great that the opposite corner has COACHK in it, another single letter in an odd place. I also keep on misparsing MADEGREE. "I made gree, Ma!" Hmmm.
The NW was the last section to go for me. I had refused to enter THREE at 2D: [This clue] + 1, which would have made things easier for me, I imagine. Instead I finally saw through 1D: Feature of Algeria and Egypt (SOFTG). How many times? HOW MANY TIMES??!
In any case, there are some great entries here with FREEMIUM, BROHUG, SPRINKLE, and GOODDOGGY.