As someone who has fond, if hazy, memories of Dan Simmons's Hyperion (and the residue of a crush on his cloned John Keats), and who enjoys most things ancient Greek, I was anticipating much pleasure from his Greek mythology and science fiction mashup novels, Ilium and Olympos. Alas, the pleasure was limited. Let me explain:
Ilium is by far the better of the two books. It has quick-moving narratives and introduces us to interesting worlds (the moons of Jupiter, a future Earth inhabited by feckless, post-literate humans living out Nabokov's Ada, Mars, and an alternate Earth in which the Trojan War is monitored by reconstituted classicists for the entertainment of post-human entities who have modeled themselves after the Greek pantheon). The characters are thin and some of them are not really Simmons's, but this is mostly forgivable; it's gripping, even if it's not hitting on all cylinders. And there are several serious weaknesses: the aforementioned thin, borrowed characters, continuity errors (one character hikes the Mediterranean Basin, then a few chapters later has never heard of the place. ???), a tendency to throw in substantial fragments of poetry and prose by other authors (the robots of Jupiter's moon spend their time analyzing Shakespeare and Proust), and a lack of clarity when it comes to which Earth is which.
All of these weaknesses are magnified in Olympos, and the narrative loses its tautness to boot, making the resolution of the many loose threads from Ilium rough on the reader. Continuity errors abound, as do misidentified characters; the digitized souls of the inhabitants of one Earth somehow end up on another Earth with no explanation. Simmons begins to vomit up ever-larger chunks of other authors' poesy and prose and tries to tie them to his story, but it only comes off as attempts to overcompensate for the genre's social position. Toward the end, he ham-handedly throws in a nuclear submarine full of black holes, which distracts us from the alleged threat posed by quantum energy usage that we have spent the better part of two books focused on. The sub was dispatched to destroy the Earth by evil Muslims, natch, in a gross culture war shout-out that will only serve to date the book.
I'd recommend Ilium, but it has little in the way of a dramatic climax; this is really a two-part 1,500 page novel. If you're looking for resolution, Olympos does technically provide it, although the ending is a less than a whimper. Read these if you have a high tolerance for Proust-quoting robots, unexplained interplanetary deity battles, Shakespeare-in-space fanfic and clumsy attempts to make fiction set in the future "contemporary" by invoking present-day political issues.