The drunken movement was novel, though the difficulty I had in the game wasn't the movement/noise level, but the time limits. I rarely had enough time to even go around the house to find the items I was required to get before the cops showed up.
An idea for the late game could be some kinds of set dressing story. For example, a drunken bar fight, but the people you're fighting actually fly away and explode like the cats.
Another idea would be alarm systems or gaurds. That could be fun.