Never heard of GameMaker? Derek Yu used it to develop the punishing labyrinth of Spelunky, while Risk of Rain developer Hopoo Games used it to build giant pig-infested stages. Messhof also used GameMaker for its multiplayer stab-fest, Nidhogg.
If you're interested, download the Standard version and play around with it. If you decide it's not for you, the only thing it will really cost you is time.