I like how simple the premise is, "Climb up the tower!". I also think that celshading works really well in a tiny web browser window.
Room design feels like it throws more enemies without any overarching idea room-to-room. You start out with enemies that explode bullet patterns on hit, but suddenly that stops being the case in the next few rooms. I want a feeling like "oh god it's the spider room" rather than "fight the enemies".
Some of the enemy patters are good, but some of them don't do much and are easy kills. In my opinion, the easy kills should take one hit to kill rather than sponging 3 bullet hits. So I can decide "do I fight the big thing first or do I clear the weak ones" at least.
I liked what I played, but it didn't feel like there was enough of a level design hook.