I admit when I first as introduced to Hellsing (volume 1 of the manga) I didn't care much for him. But really, he DOES have a very well-developed character. You seem to know all about Vlad the Impaler, I'm suprised you can't appreciate it.
Alucard is a sadistic sonofabitch. He's really just trying to enjoy his miserable existence. The more sadistic he is, the more I love him. He's NOT a good guy. He's NOT a hero. And yet, he doesn't attack the innocent, even if he does attack the helpless.
I think he's basically the definition of chaotic neutral. Both hero and villain. Both moral and immoral.
Guts, however much I love him, is all about suffering. He's sadistic, he doesn't care so much about ethics, but he suffers more than any human could ever suffer. Really, his existence is far more miserable than Alucard's.
Guts is all about determination. Alucard is all about giving up. Really, a fitting pair.