Quentin is a pretty ambiguous character in Absalom, Absalom! All he really does is tell a story. But check him out in The Sound and the Fury where he gets a much deeper characterization: yep, it's the same guy.
First things first: Quentin's kind of passive. He's a patient listener to Miss Rosa's dark, violent version of Sutpen's story, and he dutifully takes her down to Sutpen's Hundred to confirm her suspicion that someone is still living there. This passive attitude also makes it hard for him to finish his story when the always-plucky Shreve tries to butt his way in.
But deeply fascinated by the Sutpen family saga, Quentin is determined to fill in the blanks. Other than Shreve, he's the most removed from the events of Sutpen's story, but he still talks as though he has some special insight. He thinks he can solve the Sutpen mystery by sheer intellectual power and rational speculation. Ah, intellectuals.
Oh, but wait: isn't that kind of what we're doing, too? Quentin is desperately trying to piece together this story – perhaps to help him understand his love-hate relationship with the South – in the same way that we, as readers, are trying to piece together Faulkner's story. Do you think that's why we find it easy to sympathize with the guy? What role do you think he plays in the narrative?