The bane of sentiment analysis is sarcasm. It's very difficult for a computer to know if "that was way fun" is actually someone exclaiming enjoyment or being sarcastic. Heck, it can even be tough for humans to tell the difference. A USC Annenberg lab out of Los Angeles is trying to solve the problem. They built their model using human annotation.
Only time will tell if they can crack the code. Some folks on Twitter simply use (*S) to indicate sarcasm, but it hasn't caught on universally. And that's a shame (*S).