I used to play and enjoy the game, and collected a ton of stuff on my account. After the server split of the EU region, though, I just didn't want to bother with it anymore. It was already a problem that I couldn't use my EU account to play with US friends, but now I had to pick one half of Europe to play with, as well. I think if they didn't do that server split then I might have still been playing the game today.
Valve/Dota lets you play with friends in any region using any account, so it's great if you have friends all over the world. But I don't want to turn the thread into a "dota vs lol" debate so I won't talk any more about that.
There were some champion designs I enjoyed a lot. Like how Veigar and Nasus could gain infinite power as the game progressed and become an unstoppable force. Or the ninja-type champs that used energy instead of mana. That's a really cool concept.
Something I never understood, though, was how quickly the metagame evolved into a static configuration of roles. In other games of this genre it seems like many different teams are viable like going 2 top 1 mid 2 bottom, trilaning (to maximize carry farm), or 1-1-2 plus jungler. You can make it work. But in League of Legends there was this expectation that in EVERY game you had to go bruiser top, AP mid, carry+support bottom and a jungler.
It was a problem for me because I wanted to do Veigar + Soraka in the bottom lane (Soraka gives a lot of mana so that lets you farm AP extremely fast) but nobody would accept this strategy because it falls outside of the "correct" way to play. That was a bit boring to me. The longer I played it, the more these expectations began to pile up and push me into a little box of correctness.
But I haven't played the game in many years now so I'm not sure if anything has changed. It'd be interesting to hear what people have to say about the current state of the League.