I really enjoyed the game, the last level took a couple of tries, but it's a nice challenge. I do like the fact that you went with the 2-directional aiming, which can make for quite a fun challenge in horizontal corridors (like the first level), but I found it a bit frustrating in some of the vertical corridors in the second level. If you want to keep the limited aiming options (which I strongly recommend since I do find it an interesting mechanic), I see two ways in which you could make this a bit less frustrating for the player: make it so that the player can also shoot straight up or down, or make the levels even more horizontal. I see that you did try this, but I would try to make the vertical paths even shorter, or include some horizontal side-paths to vertical sections, in which you could kill the enemies more easily.
Overall I think the game shows potential and I hope you do keep the locked aiming, since it made the game more interesting for me at least. Great job :D