I have not read Echopraxis yet, but I thoroughly enjoyed Blindsight. Some very thought-provoking concepts in that book.

The idea that vampires needed to take “anti-Euclideans” and the way the ship was constructed to avoid generating right angles were some great details.

Just a heads up, don't go in to Echopraxia expecting it to feel like Blindsight. When I first read it, I was actually pretty disappointed overall, and a few of my friends had similar reactions.

Over a couple of years a few re-reads, though, I've come to enjoy it perhaps even more that Blindsight, but in a completely different way. It fills out a lot of the posits opened in the first novel, without coming to specific conclusions, but it gives you a lot to think about.