I enjoy the system and mechanics you have in the game. The art is also fairly clean and simple, which works very well. Out of everything, I think the soundtrack may have been my highlight of the visual/auditory experience, due to how catchy its tune was. If you need improvement tips, I would say to check some minor collision and enemy spawning code and as Binary stated, keep weapons permanently alongside randomized rooms of some sort. This is personal preference, but I believe it would help the game to have the timer paused after you complete a room, since it just feels clean in that manner, despite only being a few seconds extra. (Personal preference: if you enjoy having limited time, and whatever happens is on the player's behalf, it's perfectly fine that way.) Lastly, enemy variations may help keep the game interesting as the player continues to play for longer periods of time.
[The reason I state collision code, is because one the bottom left corner, while I was pushing upwards against the horizontal wall, it would teleport me to the top of that horizontal wall segment, which I found very odd.]
Overall, very well done. :^)