Wow, this is just absolutely amazing!
If you told me that this was just a gb cart I'd have believed you. It's insane that you've made this in 10 days.
The gameplay is bonkers. Customizable ships? Various enemy patterns? Just absolutely mental, great job and a true SHMUP. Only the bosses, and some of this might come down to my own skill issues, I think could've used a little work. The guy(s) who fires a beam at you I found to be really hard, with little telegraphing. Very engaging, hard fight, but could be more rounded out. The other boss I found I could easily cheese by staying in the corner and firing at him with the spread gun, he could do nothing to me. All in all though, the gameplay is still getting those 5 damn stars because this is the quintessential SHMUP, in 10 days no less.
The graphics are really good, if only for lacking a smidgen of visibility here and there (but that's really the GB's limitations, so it's in line with the GB's shmups). Not enough to dock a star, so you get 5 from me.
The soundtrack and the sounds were also really nice, and I need not repeat myself on how gameboy-y it all feels, so just an amazing job overall and a big thumbs up from a fellow SHMUP fan.