Falling back on D&D alignments, Atticus is probably Lawful Neutral (lawful within the context of his order, pantheon, and obligations) in contrast to Harry's Chaotic Good. He doesn't lack all empathy for human beings, but his first loyalty is to the Earth, not humanity. Harry would probably see him as a spooky, unpredictable supernatural entity on the order of a moderately powerful Sidhe, moreso than a fellow human magic user. He's not presented as admirable, though perhaps enviable in a Mary Sue-ish fashion; his interactions with women are very much adolescent wish-fulfillment, and of course he has lots of cool powers.
For me the appeal is more about the supporting characters, many of whom happen to be gods from a variety of pantheons. As a lifelong mythology nerd, I just find the scenarios that emerge a lot of fun. I'm not all that invested in Atticus or the other main characters (who are less well-realized and more pulp stereotypes than Butcher's characters), but I enjoy going along for the ride.
For me Iron Druid is much more of a fantasy adventure story, whereas the Dresden Files are more in a horror/occult vein (and IMO at their best when Butcher steers clear of fairy kingdoms and sword fights).
Another difference is that while both series owe a lot to Gaiman's American Gods (and to a lesser extent, his Sandman graphic novels), the Iron Druid universe is more genuinely polytheistic, whereas the Dresden Files are dancing around a basically Catholic worldview. The Carpenters are the paragons of virtue, the best refuge from more or less everything is St. Mary's Cathedral, and Harry is classic witness-bait with his "I'm not good enough for God's love" complex. Such a universe is of course more concerned with good and evil, whereas Atticus frequently points out that he and most of the gods he traffics with are products of the Iron Age, when not even deities were expected to be virtuous or infallible.