He's not leaving YouTube, he's leaving some of his channels to focus on some of his other channels/shows and things outside YT. Good on him. He made it big with YT and now he's moving on - considering he started =3 in his college dorm room and has since had it grow so large as to have celebrities on a few times (Robin Williams being the biggest name, iirc) then, yeah, I think he's done quite well.
He wrote, produced and hosted the videos and now he's going into acting. (Also, freaking My Favourite Martian was fucking great! - bar a few songs.)
Frankly, I can see why some hate him, but I think he's great, so... go him!