It's always been bad since they made the new client, but since around 2 patches ago it's been so much worse. Everything is horribly laggy, at times it's so laggy I literally can't even accept the ready check because the damn thing doesn't even appear untill I already got a time out for it. A bit ago I literally didn't even hear the sound effects of it and was just suddenly kicked out of nowhere for "declining" ready check, and after that a message that there was an error with displaying the ready check. I just came from trying to start a game but the client being so malfunctional that I couldn't even get into lobby.
On top of that even if you DO get into champ select it's so damn laggy as well. Rune pages randomly get deleted, when you try to make a new one on the fly it's so laggy that you can hardly even finish changing one in time. Skins randomly get deselected, summs get defaulted to heal/ghost all the fcking time. Or you actually manage to edit your page, press save and nothing fcking happens. Game starts and you're playing with the wrong rune page.
Then you think you're finally done with their shit, but no. Instead you get a loading screen that literally dissapears only to greet you with a "game in progress"
Now this is fixable, but really shouldn't be happening in the first place. Then you have to manually close league's processes and re-open league again, only to get some other random error when you try to reconnect again. "Game no longer exists" is a fun one too, when you have a premade friend that confirms to me he's still in the game.