lack of depth/width
The game has been sort of blah for me lately as well. I was thinking a lot about why, why the excitement to play matches has waned. The answer for me is, the game is not that deep anymore. Since it lacks many options, it is becoming repetitive. Assuming a game where everyone knows what they are doing, if you can not handle the other team's engage; the game is over. That alone limits basically everything other than hoping the team with the good comp sucks. Even the guys who get paid to play, have been approaching 9/10 games the same way for over 2 years. You can safely (and cynically) otp Miss Fortune to platinum if you so choose.
tl;dr - There are a lot of champs, but not a lot of ways to win if the other team rolls meta; and doesn't stink.