I can tell within the first few hours from the overall personality and feel whether a title clicks with me or not. I usually stick with it, though, as I haven't encountered a truly unplayable game since the NES days and I only buy games that I know have something interesting to string me along for the ride. The only time I will really drop something is if I bought it for pennies on a Steam sale out of sheer curiosity and I'm finding that it's just not worth the time.