Blackbeard is so wild. Just the facts that the real Blackbeard himself is Oda's favorite pirate and the discovery of his ship being what caused Oda to start writing One Piece are huge indications that Blackbeard is definitely one of the most important characters in the series.
There's so many interesting things about him:
1. He gave Shanks a scar and doesn't seem to be afraid of him
2. He defeated and subdued Ace
3. He shares similar ideals as Luffy, but he's every bit the opposite.
4. Luffy's rubber powers naturally reflect everything, Blackbeard's naturally absorb everything
5. He used to have a claw weapon
6. He can use two devil's fruits
7. He's got a D. in his name.
I just really like Blackbeard as a foil to Luffy. They both share the same views on One Piece, its existence, and the need for people to dream, but they both have completely different ways of living out those views. Luffy would never ever kill a crewmate, but Blackbeard had zero qualms about doing it to get what he wanted. Luffy's always said that freedom is the ultimate goal, but Blackbeard presents the dangerous situation of a bad man gaining unlimited freedom.