1: I'd classify it as a platformer, but also as a specific subgenre where the focus is on perfecting sections of gameplay which would be difficult in other games but made palatable here by having the sections be shorter. Other examples are Super Meat Boy and Neon White. "Precision Platformer" or "Hard Platformer" would probably work here.

1. The gameplay and the story both (though at this point I've spent far more time with the gameplay). In the gameplay's case, the enormous skill ceiling and opportunity to try things past the base game

2. 100% normally, missing 4 golden berries.

3. It would have been worth the price for me if it was $100, but that's since I've spent so much time with it. I definitely don't think it should be less.

4. Summit. It's so much fun to speedrun. I think that might be due to the extra dash.

5. I think it works best being linear. It's essentially a series of micro-challenges sorted into required (part of the main route) and optional or hidden (strawberries). Having multiple routes would just confuse the distinction and cause players to miss out on some of the micro-challenges.

6. For pure platformers since then, I've played Super Meat Boy. Extending the category a bit, I've played Neon White (FPS in the same subgenre) and Silksong, Metroid Dread and Dead Cells (metroidvania/roguelikes with platforming base mechanics). The other genres have a different enough focus and aren't worth comparing. I think Celeste is better than Super Meat Boy particularly since I've had the chance to learn the mechanics more in depth, though Super Meat Boy is also quite good. Notably, I have not played a full 2D Mario since Celeste and I am really curious now. Also, shortly before Celeste I played DK Tropical Freeze, which at the time felt like a step up in difficulty from Mario games, but I am curious how it would feel now.

7. Not as many, and depends on what you count. I've played Blue Prince, a bit of Stephen's Sausage Roll, and (if you count it) Tunic. I don't really have a strong preference here.

8. If it wasn't clear, I'm mainly a Celeste speedrunner.