Obata's first work was Cyborg Jii-chan G, which was the only published work he also wrote. After years of teaming up with various writter's, he got his first hit with Hikaru no Go, about a young boy who learns to play Go with the help of a ghost.
His seminal work, however, is Death Note. Incorporating a certain amount of punk sensibility to a dramatic, grandiose, gothic look gave Death Note a different feel from anything else being published at the time. After wrapping up that series, he did a hadful of one shots and a short run on an alternate version of Blue Dragon, dubbed Ral Grad.
As of now, he's teamed up with Tsugumi Ohba again to create Bakuman.