Absalom is a daring figure—even though he's doomed, he deserves some admiration, despite doing some things that are pretty disturbing. He reacts intensely to his father's refusal to punish Absalom's half-brother, Amnon, for raping Absalom's sister. He kills Amnon and flees into the wilderness. That might not exactly be "heroic" but you've got to give him props for guts.
The literary critic Harold Bloom says that Absalom is a lot like David except without David's good luck. Which is totally true: Absalom has all of David's charisma, his good looks and his verve, but somehow it doesn't manage to work out.
What he lacks is God's blessing. Despite Absalom's good qualities and his popularity with the people, he just doesn't have the Powers That Be on his side. He rebels against his father with wise counselors and the people of Israel supporting him—but it just doesn't take.
We can't deny: there are also disturbing aspects to Absalom's personality.
When Absalom takes Jerusalem, he goes into the palace and has sex with his father's concubines—a sign that he's really bent on seizing authority. There's no going back—he's crossed his Rubicon, so to speak.
Here's the passage:
Ahithophel said to Absalom, 'Go in to your father's concubines, the ones he has left to look after the house; and all Israel will hear that you have made yourself odious to your father, and the hands of all who are with you will be strengthened.' So they pitched a tent for Absalom upon the roof; and Absalom went in to his father's concubines in the sight of all Israel. (2 Sam 16:21-22).
It's an unsettling detail—a little too much of a Freudian case for comfort, we suppose—but it's unclear whether this is supposed to put Absalom on a lower moral footing than David. David, after all, refused to punish the rape of his own daughter, whereas Absalom is doing what, perhaps, the new king would be expected to do.
Absalom, for all his ambition and fire, meets a pretty absurd end. Possibly out of vanity, he refuses to cut his hair more than once a year. During his battle with David's army, he gets his hair caught in a tree, allowing Joab to execute him (against David's orders) by sticking three spears straight into his heart. So, the book seems to argue, you can have flash and dazzle—but, in the end, there needs to be a more substantial basis to your character and your plans than that.
Also, the name Absalom means, "Father of Peace."