Fun little game you did there - I got to level 19 on my first try. :)
What's the big dino for? I thought this to be a boss, but the gates opened after defeating the minions.
Maybe the bullets could be a bit bigger, or read better, and some screenshake would be good for the juice/feel.
The dungeon crawling aspect with the single rooms is fun. Just like Zelda 1 or Binding of Isaac.