I don't know Hayden's other work but I have heard he had potential. I just know that almost no actor could have saved Anakin from George Lucas' writing. I don't know how the hell Ewan McGregor managed to save Obi-wan and stay so likable and awesome throughout the movies, I can't think of anyone else that was able completely salvage their characters aside from maybe Ian McDiarmid... Ian McDiarmid basically embodied the Emperor in an almost classical acting style. But Ewan made Obi-wan one of my very favourite Star Wars characters in a trilogy with so few good characters, so I have to say that if there is a star of the prequels it is him.
It's funny because the Star Wars movies in the big picture are supposed to be about Anakin's journey, but I feel like the prequels are Obi-Wan's story, and that leads directly into Luke's story with Anakin serving as a backbone or catalyst for both.
Anyway, I think Hayden's acting job was on par with the horrible directing he had to deal with. He had a few dark scenes where he did a good job conveying the inner demons of Anakin but 90% of his dialogue was stilted and the "romance" was high school film quality.