Nice game! My elaboration:
1. My overall impression was a fun little Celeste-like with a solid design.
2. The gameplay was basic but effective to the game's design. I feel like the game could expand on the mechanics to introduce new ways to overcome obstacles, and to reward the player for discovering these new ways.
3. The graphics and art are simple and somewhat charming, with that classic minimalistic pixel art style. I would way that the colors are a little flat and lack much depth, but this does go with the style the game is going for.
4. Some of the sublevels in level 1 were just... a little hard. Maybe keep all of level 1 fairly simple and tutorial-like (without dragging it out), and bump up the difficulty for the coming levels for a better difficulty curve.
5. I think you can make the game's design more unique, by coming up with creative ways to manipulate the core mechanics and make several ways to solve a problem. This goes for all platformers imo: You can analyze how the player would normally try to overcome an obstacle, then branch out and think of other ways that may compliment the normal way. The player will feel rewarded for figuring out a fresh perspective to solving a problem, instead of getting frustrated and wanting to quit. Also the sliding can get kind of annoying sometimes, because I'll accidentally run into something when trying to move on.
6. Don't think I have any favorite moments... I liked it a lot when I was able to finally beat that level I accumulated over 100 deaths on!
8. If 5 is extremely enjoyable, I might give this game a 4 rating. Mostly because it has everything a decent platformer does correctly, but it doesn't draw me in and make me want to keep playing for hours.
Please feel free to check out my game: https://wasabiiii.itch.io/grass-elemental-demo-demo
Good work!