Beautiful, absolutely stunning! The three generations and two time periods were perfectly delineated and distinguished - the feel for the language of Godric and Salazar's time was right on pitch. Harry's faltering marriage and slow progression into sexy dreams was totally realistic, as were the kids (including James being mainly abroad, running through fun and girlfriends!). I love you sorting Lily and Scorpius into Ravenclaw!
The underground chambers and scenes were beautifully described, very solid and believable in many ways (the herbs gone to dust, the bare stone) and yet unearthly enough in other respects (the curtain--a Veil?) to bring all the necessary magic to the scene. More than that, a medieval enchantment that was (like all the Hogwarts Founders parts) pure Arthurian gold. I also was very much reminded of some of Andre Norton's work in the combination of concrete vividness and almost scary beauty.
I adored the conversations with Snape's picture. (I want one.) The mention of Hogwarts' Greatest Headmaster being gay. Heh! Great use of "peri-textual" or post-textual information. And Harry bringing--inviting--the photo-Snape upstairs at the end was a sweet note to end on. *wibbles* That and the whole family photo review, just as at the beginning, brought the sweeping saga back to Harry's heartfelt desire for a cozy home and family. All is well!