League's client is still awful
League has never had a good client from day 1. The fact that a new client was only released little more than a year ago, with Adobe Air being used for so many years doesn't set a good precedent, but even the new client is buggy and incredibly slow. While it works much better than Adobe, there are still constant in lobby crashes, invisible missions, and somehow the client takes up more disk usage than other games or applications that are easily more intensive than League.
League's servers have vastly improved, and connection issues are practically no longer existent when playing on any decent internet connection, but the client desperately needs to be updated again. Loading screen timers are unpredictable, and while crashes are not frequent, they do occur regularly enough that penalization for AFK behaviour is becoming a possibility.
Dota's client runs quite smoothly, and I haven't yet experienced any kind of lag or crash while playing, and while League is undoubtedly the better game, when it comes to making a good client, Dota is still vastly ahead. Maybe instead of focusing on reworks and pumping out changes, Riot should look into making the overall experience of the game more pleasant.