Good game! I realized there was a metapuzzle almost immediately (also that's part of how I found it in the first place), got inklings of what it was near the end, made a second copy of the file, figured out Puzzle 11's gimmick pretty quickly because I happen to know the names of plutoids off the top of my head, and had a lot of fun. It took me most of an evening.
If I have any criticism it's that Puzzle 1 is (still) too hard, but, maybe that's the intended difficulty? There's definitely other stuff in here where you'd need to know trivia to connect it to the theme, like with HAUMEA and QUARTZ, and the theme for Puzzle 1 can't be too obvious. I ended up solving 12 first by guessing and then going back and doing 1.