It kind of depends on your point-of-view and interpretation. Prospero is viewed by a number of critcs as flawed. He can be seen as meddling and vengeful: meddling in the affairs of his daughter, vengeful towards anyone who crosses him, even former "friends".
On the other hand, he does show signs toward redemption at the end of the play. Some critics have argued that Prospero "must learn to control his anger with reason and to temper his sometimes arcane studies with the practical art of government before he is ready to return to Milan as duke, and that once he accomplishes this, he resembles the ideal Renaissance Man."
Is he sympathetic? Those who recognize their own flaws may find him to be so, especially if that reader or audience member has tried to make amends for wrong-doing. As Alexander Pope famously said, "To err is human; to forgive, divine."