1. You see where you keep repeating those trees? Mix it up, put other tree combinations in there. It's possible to make two, four, or even five trees standing together with some crafty tilework.

2. That blue line is a very obvious line of symmetry. If you mix up the eyecandy so that it's not so symmetrical on both sides, it'll look a lot less boring.

3. Too tile-y. Make it less tile-y.

4. For the love of god fix this

5. As an afterthought, seeker powerups are generally frowned upon in levels. Don't use them unless it's like the only source of seekers or something.