portal
one of the steam for mac games is portal. portal is a first person shooter except your gun shoots holes instead of bullets. a blue hole and an orange hole. you jump in one and pop out the other. you use this teleportation trick to solve puzzles arranged by a neurotic central computer obsessed with cake and delivering some of the funniest zingers you've ever heard coming out of a video game. which are really very distracting when you're trying to dodge laser beams and pools of acid. portal is awesome from start to finish and if you don't agree you must be fucking stupid.