Definitely an interesting basis for a game, there's some nice visuals and a good basis for an enemy, not super specifically stylized but better than nothing. On the same topic as graphics the guns you sue have an interesting design, a nice little visual that's setup in the camera view, plus what looks to be, from the screenshot, a nice overall model.
While the levels did get a bit repetitive, obviously since they were the same thing, it was a little interesting and definitely made me wonder if there could be something else to mess with to mix them up a bit. For example wave defense style, or Zombies style etc. gameplay maybe.
Overall it's not a complete game, but it was definitely an interesting (almost very frustrating) experience to go through it all, mainly because of the final level I'd say. That one added some nice variation overall. Except for that freakin cube.