The last few matches I have been kicking ass and taking names, usually despite my teammates

And Every **** Time(tm) one of the opposing team complains that maokai is OP or "sleeper OP".
Now normally I'd just dismiss this but it keeps happening; so I turn to you dear forum.

Is Maokai really so OP or is this merely sore loser crying?

Sore loser cying. Not to sound harsh, but that's what people do, they can't blame themselves, therefore they say X is OP. Example, if they somehow get stomped by a Yorick (pre-buff) they would say Yorick is OP.

I've recently bought Maokai, and after a few games with him I think he's perfectly balanced. The knockback could be a little more clear (launch into the air or into a wall) cuz atm i can hardly tell if i knocked them or just slowed them.

The biggest thing about Maokai is you need to have faith in your team mates, just like amumu. if you engage and your team doesnt follow, you're gonna get wrecked. But if your team runs in and stays in your ult, you'll have a better chance of succeeding.

did u build ap or tanky? cause it's kinda weird for them to be calling the tank op. i wouldn't say he's op but he's pretty **** strong and a stun slow damage reduction and a sapling that doubles as a mini ward.