So, the concept is really cool and it's done pretty well, but I still had some fun-related issues ^.^'
First of all, the other guns seem pretty redundant outside of the boss battle. Same with the jump upgrades. It wouldn't even be a problem if there were more enemy types that require more hits to kill in the later areas or if there were rooms that require going up to the ceiling to avoid some obstacles instead of just sticking to the floor level.
Another thing is the escape sequence; the game is easy and the auto destruction part is even easier than the rest of it, because 15 minutes is way too much to feel pressured. Even having just half of this amount of time would be a bit more than enough.
But every other thing about Infinitroid is just great and it's really hard not to enjoy that Atari-esque demake of Metroid :D