My experience with Echopraxia is that it's significantly more confusing and complex then Blindsight. There are chunks of Blindsight that go over my head, but in general you can get the gist of it from context (and was rewarded on rereads as things progressively became clearer). Echopraxia somehow was not able to navigate the tension between ambiguity and outright confusion. I believe Peter Watts has acknowledged this as a problem in Echopraxia and spent a Reddit AMA explaining to readers what the plot was.

I do need to reread Echopraxia though, and perhaps my opinion will change after that. Blindsight was brilliant enough that it deserves the extra effort to appreciate.