I watched the Champion Spotlight on Maokai last night and here are some of my first impressions on Maokai, the Twisted Treant.
This hero looks rather interesting, but I don't know where he's going to fit into the current meta game. I suggest watching Phreak's spotlight to give you an insight into his abilities and play style. I think he is going to be played like a tank version of Teemo during downtime and during team fights he is going to function as a fight disturber, similar to Malphite. Instead of giving him a heavy CC though, they opted to give his ultimate a defensive feel with offensive potential.
This champions skill cap is going to be fairly high. Knowing where to put saplings, knowing where to drop your ultimate, when to break your ultimate. These are very crucial things that will all effect how well he is played. Disrupting the enemy carries day will be the easy part of playing him, the hard part will be effectively defending your team while you do it.
All in all, I will probably pick up this champion and try him out. He looks like he won't need that much to become tanky so he may be opted as an AP champion. We'll see how things pan out though.