A side-scrolling platformer is something we've all had experience with, therefore I recommend it as the genre as well.

I will be thankful if you all choose some gameplay-related keywords:
unarmed combat; melee weapons; ranged weapons; stealth; psychokinetic powers; time control; gravity control; light or shadow control; magic; shapeshifting; summoning; gods' influence; jumping onto enemies' heads; alchemy; teleportation; vehicles; other (specify).

KRSplat, thanks for your offer. Music and sound will for sure come in useful. I'm not sure about programming though. Do you have any experience in game making and are willing to replace me as the main programmer? Because it's not like I'm very interested in programming it anyway and I realize GM is not the best tool to make a game, I just decided to since there was no one else who could do that.