Well, your picture is not really isometric. The wall and the top of the door like FreshSheet says is wrong. Isometric lines are 2:2 to make straight lines. If you don't understand this make a WIP thread for this piece, k.
Yes, I drew for an isometric tower, but I have not much experience in isometric.
This looks great, although I'm not a fan of the sprite, and I think the walls could use more detail like the grey walls have.
Also, it's not isometric in a few spots along the top of the grey wall and at the door, not sure if this is intended.
Although I agree that this needs more work, there's something that I liked about this one. But I am baised because of my love for Silent Hill.