Hmm, it was alright, but compared to previous games from you, it felt a little underwhelming, though I understand that it might be due to it being a prototype, so perhaps I'm being a bit unfair. But in that same vein, it is a prototype, so I feel like I should try to give as much feedback as possible to make it become a great game.
First off is the controls: they default to mouse-only controls, which I, and it looks like many other people, get very confused by since it creates a very awkward way where you need to move in weird ways just to aim at the enemies. I thought maybe the weird control scheme was on purpose to make it more challenging or something, like a fumblecore game, but luckily I was able to switch it to control scheme number 4, keyboard and mouse, which I highly recommend you make become the default since it seems smooth and logical for a shoot em up like this.
The general gameplay, while functional and smooth, seemed a bit overly basic. Unless I was mistaken, it seemed like all I could do was move around and shoot. No special abilities, no bombs, no grazing, no excitement derived from trying for a higher multiplier, nothing. Don't get me wrong, the enemies did seem to have a good variety to them and the levels progressed well in terms of difficulty, but it was just a bit bland. The levels were just static images grayed out, and the waves were just teleporting in scattershot: nothing like the excitement of scrolling shooters that take you through all sorts of animated backgrounds and waves entering in all sorts of interesting patterns (again, though, perhaps this is just missing because it is a prototype).
Finally, and this isn't a big one and only my personal inclination, but I don't really like it when shooters utilize an upgrade system: I prefer for the experience to be balanced around a standard loadout, it being solely the players own skill and style that gets them the victory, instead of having victory chained behind bullet sponges that you need to grind to level up just to be allowed to win against.
There is certainly a lot of good about this game: the menus were nice and animated, (albeit a bit overly black in terms of palette), the enemies and bullets were easy to see and had tons of variety, and the core gameplay, while basic, seemed solid and smooth. While I had plenty of nitpicks, the number one thing is that I just feel like it needs some sort of special something to add to it, some sort of unique hook. A prototype is usually created to sell a unique gameplay mechanic or loop to see if it's got legs: this didn't seem to have any of that, just the boring basics. The game's like a plain scoop of ice cream at the moment, I just need some sprinkles and a cherry on top now, and I do have faith that you can deliver it based on your repertoire, so I'll be looking forward to the future!