Great concept with the random gem combinations.
I personally think the enemy spawning should get tweaked a bit. I found myself often sprinting past spawn points to not get one spawned on me and the enemies tend to build up into massive hordes. As you mentioned responding to VKChiuselli, the movement delay when shooting makes the enemies really difficult to fight.
If this idea were to be expanded I'd like to see the effects of the gems feel even more impactful! I think you have the basis for a super cool rogue-like game here. It kind of reminds me of things like Zelda randomizers.