League will be imbalanced during preseason. It's ok to quit and wait for things to pan out.

Yes, Riot changed a whole lot and League might look way different to you than it did in Season 2 or whenever you started. The game would get stale and lose people if it stayed the same. Different does not mean worse.

If you don't like how things are going, it's ok to quit. Nobody is going to blame you for not liking how it is now, and it's expected that you don't stick with a game forever. Feel free to check in on the changes when the season starts, or even the season after that. Your account isn't going anywhere and you can come back any time.

Want to voice your opinion on the changes? There's no need to threaten quitting. Just explain exactly what you think is wrong, and suggest changes that you think will make it better. Complaining without presenting a solution is called whining.

Don't know what changes Riot has planned already? Keep up to date on the PBE by checking Surrender@20's PBE notes, and see what Riot has to say about things with the Red Post Collection. Want to see what Lyte says, especially on the Player Behavior Initiative? Ask him on his ask.fm page and read through his past answers. Lots of information can also be found on the League Support Site.