Hi! Thank you for playing!
Of course this is easy to say, but we did have more plans for the game - unfortunately the 48-hour time period got to us so we didn't get to implement a lot of things we had in mind, including but not limited to: more upgrade types, special weapons, more enemy tops, hazard that'd appear if you killed specific enemies while on the wrong tile, things like this. I agree as of the bullet hell part where it's mostly easier to just kill enemies right off the bat, however, for some of the people who have been grinding high score waves and got quite good at the game; this didn't happen for them until approximately wave 25~+, at which point it was getting stale due to lack of content anyway :D
Either way, thank you for your feedback, it's much appreciated!