Best Geo-Mod (Red Faction)
Almost no one still uses Geo-Mod as it existed in Red Faction, and with good reason: it's almost impossible to design your game where players can just blow up a wall or a floor instead of going on an extended mission to meet an NPC to get a key to unlock a door. But the brave folks behind Red Faction pioneered the incredibly awesome, if not particularly convenient for developers, gimmick. Waste time blowing everything around you up, find crazy new ways through levels and missions, defy physics by knocking down a load-bearing wall with no effects? Doesn't get much sweeter than that.
Worst Blowing (Nintendo DS)
Nintendo DS had one very good gaming gimmick (the 2nd screen) and one very awful gimmick: blowing. Yes, anyone who's played Diddy Kong Racing or Mario Kart DS or any other number of games will remember how bad and dumb the blowing feature was. In attempting to make some fun handheld games more "immersive," Nintendo made a lot of people look really dumb and feel unnecessarily dizzy by making you puff precious breath at the DS microphone.
Just picture it: there you are on the subway, casually playing your DS. You notice a cute person sitting across from you. You smile. They smile. You press your face to your DS and puff out your cheeks and puff like an idiot because the sensor never works that great. You look up. The cute person has moved and is now sitting next to the sleeping homeless guy, because he seems like a more acceptable person to interact with for the reminder of the trip. Also, you just missed your stop. Dang.