Most of the flaws, but not all, are tied to using a bot scripted language to determine if a tweet is a happy or sad tweet. While this sounds simple enough how would something like "I love you to death" score? It is a very happy tweet but death is usually scored as a negative. Meanwhile how does a bot deal with sarcasim? "I just had the best xp of my life, in traffic for two hours", is a strong negative emotion but would probably count as positive. Plus things like weather can impact what a person tweets but hardly impacts a persons over all happiness level.
Right away Z points out that too many people are taking this simple GIS project and claiming it is finished geography. GIS is a great tool, it is not a finished product though. Geography, and common sense with some critical thinking, is needed to properly analyze GIS output.