I wouldn't call this game hard, more frustrating. I lack a sense of control, because i couldn't move in the air. Every time i get launched up in the air there's a a 50/50 chance that i fall on a side and can't get up.  Besides that I've had multiple moments where I bumped into a small incline and just rolled over. These moments feel unfair. For future projects look into adding things like coyote jump or similar more relevant tricks to add to gamefeel.

The art is nice and definitely an improvement on previous games. I liked the lava shader the most. Though i think the art could have been used better. Because of the square shape and the rapid changes in the map it really feels like a game world. I think it could be improved on with more organic shapes of map and maybe mountains to separate the biomes to make the transition smoother. A world outside the playable map would also go a long way. and/or with a skybox.

I hope i helped you a bit further with your game dev journey with this feedback. Keep going at it!