It's a very simple game, but a good start..

A few suggestions:

* Set the "simulation space" of the particle system to "world" instead of "local"
* Also use "size over lifetime" and "color over lifetime" for the particle system to have the particles fade out and shrink
* Add some kind of background, even subtle something is better than nothing to give the sense of movement. Right now if you jump and there is no ground, you don't know if you're moving or not, or how fast you're moving
* The levels need more work and polish
* Most levels you can simply jump/fly over or run under the obstacles
* In one level a big red box comes at high speed from nowhere and moves very strange

Good luck