He's been around before G4TV. I don't know if he really owns it, but he's on there quite a bit. He's done shows like Reviews On The Run/Judgment Day, and of course Digital Playground as a game reviewer. He's also done music for several games. I think he did Cool Spot, Earthworm Jim, Advent Rising, among others. He did work on the sound design in the Metroid Prime games, too, and has probably written music for/produced many other games as well.
Tommy Tallarico on WikipediaI guess part of where he's gotten on my nerves is that I sometimes really don't agree with him, and when he does like a game that I do too, he can't be serious (he liked Wind Waker because one character in the game has snot hanging from his nose...o_0). Perhaps his craziness is part of his onscreen persona (he is talented enough to be respected, I guess). That craziness is probably more evident when he's with his more serious reviewing partner, Victor Lucas.
But, hey, Tallarico's set up this Video Games Live concert, he can't be all that bad.