2D Shooter Base

I like the way that your modifications are headed, here's a couple comments:

1. As a tip, when making new levels, try to make sure that they're significant and unique/different from others in some shape or form. Adding new enemy types, challenges, or obstacles can help with this!
2. I notice that two of your modifications are art related. I'd highly recommend putting some time into making your own sprites and getting more experience with game development art - this is a great chance to hone your skills.
3. Along the lines of #2, take a shot at making some custom music! A good soundtrack can really enhance the overall gameplay experience.