I know it's presumptuous of me, but I can't help feeling that everyone who's drawn to Snarry must have some sort of kink for power dynamics. It's there in full force during their first confrontation, and it only gets fiercer as time goes on and their mutual loathing spills over into the public arena. It's the language they speak to the exclusion of all other languages, at least with each other.
And yes, there was a lot of maneuvering and explaining and sacrificing and what-all in DH - a lot of sound and fury signifying nothing - but the emotional payoff wasn't there. One thing even JKR would have to admit Snape brought to the books was intensity. He was the link to the Marauders' era, the good/bad character who'd suffered and who'd inflicted suffering, the one who occupied the middle ground between the villain and the hero. He was equal parts noble and malevolent, and more than either Voldie or Harry (whose fates never really deviated from the standard pattern), it was Snape whose story needed to be addressed. Snape whose soul needed to be judged. Because he was the one who really represented what it means to choose.
Uh-oh, it's late and I'm tired and I'm starting to drone on. But you know what I'm trying to say *g*.