Very, very close to being mind-blowingly amazing.
It's set at least 10 million years in the future, when humans have become immortal gods. Some humans at least - the clone members of the "thousand families." It starts as youngsters of some of the families (already hundreds of years old by this point) are growing up, taking part in ritual snowball fights. The action starts when Alice of the Chamberlain family (one of the oldest clones) returns home to Earth with some very bad news.
Despite being fairly short this does feel like an epic. It stretches over thousands of years, the ambition is immense and there's some great character arcs going on. Unusually, it gets better the further you get into it.
The most impressive aspect is how these unthinkably powerful humans are portrayed. They don't need spaceships to travel, but it's not as if they're flying through space like Superman. They still haven't broken light speed, and journeys and battles take hundreds and thousands of years relative to the relatively normal humans on nearby planets. They're made up "talents" - different abilities created from normal matter, dark matter, dark energy and exotic matter. Indescribable, yet described really well.
It reminded me of two books in particular (well three, if you include Marrow, which is Robert Reed's first book) - Olaf Stapledon's Starmaker and Dune. Starmaker's a fairly straightforward comparison because it takes the long view of the universe, and deals with god-like being who create new worlds, galaxies and universes. Dune because of the ruthless manipulation and breathtaking trickery going on between massively powerful families.
It's not perfect - I felt the addition of some of the characters towards the end was a bit redundant. The start drags a bit and the lead character Ord isn't very interesting (clones, eh?) But very impressive stuff overall.