That was a cool idea! a good base to build upon. But as someone pointed out already, it needs more challenges, something for the player to do (even if it is dodging some bullets) so the navigation doesn't feel stale, also more puzzles, less back and forth and color the rooms more clearly, maybe the numbers will be colored too so they know they open a door in that room (for instance red numbers open the codelock in the red room, something like that). Oh, and of course, eventually you'll need enemies.
Oh, and allso you need diagonal movement so that you can traverse the rooms more fluently. But as I said, you have a good base already! You can make something like The Binding of Isaac. Good job so far! keep it up!