Hi there, I had a quick play through so that I could give you some feedback.

It seems fine for an early test, but the game feels a little static... I liked the little touch where some plants sort of sway when you run past them, but I found it a little odd that since the player runs so fast; it wasn't noticeable until I played through the second time, when I was trying to pay more attention to small details.

I don't mind the visuals and think they work, but I think a little more animation would be helpful. I think more frames of animation for the run, lifting the legs and timed better for the movement speed would help bring it together, as well as some sort of idle animation.

I found the difficulty fair and quite forgiving with the respawn points, though maybe too forgiving... It makes sense that there isn't a lives system, but have you considered something like loosing a single gem for every respawn? It might help with getting the player to try again to see if they can get a non-death run for each level.

Though I didn't find any game breaking bugs, I did notice two collision related things that I thought I should bring to your attention:

I found that if you are on the far edge of a platform, the game seems to detect a fall, but the player is still on the platform, so they sit there in this pose:

My assumption is that you are using a ray cast to check if the player is currently touching the floor, but this doesn't take into consideration whether the sides of the bounding box are still in contact with the platform. I don't use Unity, but I would check if there is an "onFloor()"-kind of command related to physics/collision detection or if you're able to grab a current list of intersections/collision-points with the player bounding box and check if any exist at the Y location that exists at the bottom of the bounding shape.

I only noticed this one once, in this specific place, but if you stand on the wooden platforms and run to the left, the player will do a little jump as it crosses back onto the grass.

I'm assuming that the top of the grass and top of the wooden platforms are ever-so-slightly unaligned, with the grass being a pixel or so higher, so the player actually intersects with the corner of the grass and slides slightly upwards, leading to a jump. It's not a big thing, but I thought I should make you aware of it.

With the current build of the game, unfortunately I wouldn't say that I found it very fun, so if I stumbled onto it randomly; I probably would play the whole game, but I think it might have potential. Have you considered adding some enemies? I don't mean to fight, but to avoid, like the steam. For this level, I was thinking large bugs, mushroom men and so on. I think it would be more interesting to have some level themed enemies and make the player wonder what's going to be in the next level. Maybe you can bounce off some or use them to actually get to other locations. ...well, just a thought.

Hopefully some of that feedback was helpful.
Best of luck :)