Somewhere near the beginning, the likely ending was readily apparent. However, the route you took to get to it was anything but :). Fantastic story - loved it.
Snape's relationship with Lily jr was completely wonderful - actually, with all the kids, and even the non-relationship that skirted around James jr was appealing in a way. I found what you did with Draco incredibly satisfying, with Snape as a mentor helping develop him into someone quite human.
I'm an absolute sucker for the stories that span decades and pile on the pain in the middle. Harry, avoiding Snape for the first few years of Harry's marriage to Ginny. Snape, almost entirely avoiding Harry for decades, all that loneliness and difficulty for both of them.
I'll admit a personal mild, er, something - not dislike, nothing so strong, maybe just that it strikes me as a little unlikely? - for the approach that has so many of the central male characters in a verse fancying the lads. Snape, Harry, Draco, Albus jr, Teddy Lupin, Sirius and Remus... Still, the last two are practically canon, and with wee Al and Teddy one could easily argue genetics, and you'd pretty clearly established Draco as shagging anything that moved. Heh. That was immense fun, actually. I think it wasn't so jarring in this story because the discussion of sexuality was so central to the primary relationship, so there's sense in focusing on secondary relationships that are same-sex and related in some way.
Hah, I think I just talked myself out of having a problem with it in regard to this story :D.
Anyway. This was gorgeous, a bit epic (in a good way!) and I loved the slow and obstacle-filled development of the romantic side of the relationship.