One word: "Slick"
You seem to have taken a Space Invaders aesthetic and combined it with some wickedly fun bullet pattens. The neat evolving mechanic makes this game stand out from other NG shooters (though the king of NG shmups for me will always be Raiden X... if that's still around, check that out!).
While being a curmudgeony neophyte shmup fan (only really getting into the genre with the purchase of my Sega Saturn), the gameplay I can attest is spot-on. While I would have liked to see what it would be like to move with the arrow keys or something else, the mouse movement works for what it needs to do.
The music, while not entirely my cup of tea, had some genuinely good tracks, and complimented some of the action very well.
The people who say this needs "better graphics" are idiots, plain and simple. The game has an aesthetic, and that's not something "graphics" can improve or detract. I am not entirely sure what the whole procedurally-randomly-generated enemy thing was all about, since after a while i only saw the same types of enemies. I dunno, but hey it sounds cool.
The only real complaint I could possibly have is that in the early levels, things are so mellow that you can pretty much stand still and beat the level. This lasts roughly the first third of the game, until you say, get your pods, or the first 'boss'. Now, the evolving mechanic keeps this from getting to be a drag, but you might lose potential players since it doesn't "start out with a bang", so to speak. If you are worried that this is a problem; don't, if my 9 is any indication.
The later levels are frantic, and I appreciated the inclusion of a screen wiping bomb... and was impressed by the clever introduction of the walls to keep the Redrum from being useful in those lonely bullet-infested stretches.
I mentioned before the concept of "aesthetic." This game has a lot of it. Clearly the creator loves shmups, perhaps stuff by Cave, Toaplan, Treasure, or ZUN (I prefer Taito shooters myself). Heck, the WARNING siren even comes with Japanese underneath it, so clearly you knew what you were aiming for. The little touches like that might go unnoticed, but to a shmup fan, it makes the game irresistible, and a great, short, concentrated experience of fun.
Well done for such a finely-crafted game.