The Silmarillion - J.R.R. Tolkien
A reread. I have no idea what number I'm on now; the nearest guess I can make is "umpteenth".
My response to it continues to shift every time I read it. I nearly cried at Beren and Luthien (but then this is not an unusual occurrence) and the Downfall of Numenor got me a bit too.
This time around I read it in quite short bursts, which suits it well, I think: one of the things that really struck me was how profoundly un-novelistic it is. It's hard to say anything about authorial intent here, because The Silmarillion as a whole, consistent text is so much a creation of Christopher Tolkien's; but it really is a history, a myth-cycle, interested in representing a truth through symbol and literalised metaphor rather than, e.g., psychological realism. What it definitely isn't is entry-level Tolkien.
I also love the rhythms of its language, the profoundly Old English cadences Tolkien's philological background lends to its Homeric rise-and-fall narrative. Every now and then I'll discover a new reference back to those Old English sources and it will make my geeky heart sing and immediately start analysing.