The aesthetic and look of this game are top notch: the art direction really does cover that whole PS1 aesthetic well, and that nice pre-rendered animation of the mech at the beginning, oh my god, so perfect... And the music is wonderful as well, honestly!
But... the game definitely has issues as far as bugs goes. The most prominant of which probably has to be some crashes when enemies spawn in while you're locking on; it seems to consistently crash the game, which is a bummer...
Mechanically I have some complaints; the health system, as mentioned in other comments, isn't very clear, and the fade-to-black with no animation gives you very little feed back to when you're dead. I can't even tell when I'm grazing against shots or getting hurt by them, honestly.
The element of bullet-spam is nice as a "final upgrade" sort of thing (think how like, CAVE shooters handle upgrades and the like), but from the start it does feel a little... I dunno, spammy. Still, it *feels* good, and that matters more imo.
Only other issue I have is the explosion sound issue, as mentioned by Studio Lemi. Really had to turn the game down cause of it... which is unfortunate, cause the music is really nice ;;
I'm being a little harsh, but only cause shmups are important to me and I know you're doing something really cool here, just something that needs more time with. I would be beyond happy to see you work on this more, honestly. And of course, good job for making this in the first place!