Games are supposed to be fun, relaxing your mind, giving you a little time off and making you not think about work, school or whatever.
Now think to yourself how many games you played so far, 1000, 2000, 5000?
How many were joyous and made you a happier person? How many made you angry and lose faith in humanity? That's pretty much the answer as to why League of Legends is a bad game. Even if you win, you rarely get the satisfaction of having had a competetive game with skillful players who value you you for your skill and not luck, op champs or lags.