I love Tyrian, and this was pretty good as well
Great effort, I can see a lot of work put into this that some people don't realize. I've felt the similarities to toe retro shmups, as well as many differences. Not that this is necessarily bad, I'm just pointing that out. The graphics I was hoping to be pixellated(No, I don't mean the low quality) like them you've described to give it a better fangame feel.
Now for the cons.
The game over remarks are very rude.
At first, I've played it on medium difficulty and went all the way to the Fleet boss, where I got my ass handed to me repeatedly by his cheapo dash attack. (HE STILL ONE-SHOTS ME ON MEDIUM WITH THE BEST GEAR.) The hitbox for that is way too large and he dashes too quickly. You MUST reduce at least one of those aspects in order to actually allow people to even beat the whole thing on medium to hardest difficulty. So I had to go to an easier difficulty, and the freaking boss dies in a heartbeat, he doesn't even get to dash. Blarf. The final boss was loads easier than that angel freak.
Not necessarily a con, but I noticed you don't get your money back for your old stuff when you upgrade. They did this with Tyrian.
Anyways pretty good, worth trying. Good job.