A nifty little game, even if a bit janky, reminds me a lot of Doom64 with some Alien influence sprinkled in.

A few gripes I had with it though were the one time where a group of enemies pushed a guy out of bounds when stacking the doors they can't open, forcing a level restart due to softlock. Probably either make them just open doors, or add a kill field to the out-of-bounds areas if better collision isn't possible.

And the enemies just loving, loving to shoot from outside render distance, which honestly feels kinda cheap since they don't loose any accuracy at distance. It's especially bad with the first boss and the later levels where you get these acid attacks you can't possibly dodge from inside the render bubble since your hitbox is just that wide.
And so you have to resort to cheese, since your weapons can also hit far outside the render distance, making it not very visually interesting to play in the long run. With the game already being pretty simplistic on that front given the hardware blasting blindly into the darkness isn't helping it any.

There's also a bit of jank with the damage by the mobs affecting your movement momentum, which makes it kinda awkward to move around large crowds as they push you with bullets and even fully stop sometimes. But that's more of a mouse+keyboard issue since I'd assume you weren't supposed to move around much with PSP controls.
As a side note, W+D (or A) boosts your forward movement speed like in some older titles what didn't have an acceleration check for that, not a con just thought I’d mention it.
Edit: Oh, and the inventory scroll is inverted by default for the mousewheel with no ways to remap it.

But ignoring the wall of text, I'm actually looking forward to whatever might come next, with the developer moving on to a more modern PS Vita console.