Omnicron is a vertically-scrolling shmup with pixelated, NES-style graphics. We see a lot of shmups, but there are two things about this that are noteworthy.
First, your ship moves with WASD and continuously fires, leaving your other hand free to move the mouse -- and anything blue you see on the screen can be absorbed by clicking on it, mouse pointer moving independently of ship. This is good for two reasons -- blue energy charges up your bomb (released with RMB, which clears the screen of enemy fire), and the blue stuff will kill your ship if it comes into contact with you, just like enemy ships and the (non-blue) stuff they fire. This is interesting, because it means you're trying to do two, dissociated things with your hands at once -- left hand maneuvering your craft, and right playing whack-a-mole with moving blue objects.
Second, the developer is obviously a student of the form, and though the graphics (and MIDI music) are quite retro, the variety of aliens and their behaviors feel well tuned and very much in keeping with the game, a style just short of bullet-hell. The bosses are quite impressive too. Indeed, I've often played far more modern-looking shmups that are far inferior.