I have no grounding in cogsci/popular rationality, but my initial impression of LW was along the lines of "hmm, this seems interesting, but nothing seems that new to me..." I stuck around for a while and eventually found the parts that interested me (hitting rocky ground around the time I reached the /weird/ parts), but for a long while the impression was that this site had too high a rhetoric to actual content ratio, and presented itself as more revolutionary than its content justifies.

My (better at rationality than me) OH had a more extreme first impression of approximately "These people are telling me nothing new, or vaguely new things that aren't actually useful, in a tone that suggests that it's going to change my life. They sound like a bunch of pompous idiots." He also stuck around though, and enjoyed reading the sequences as consolidating his existing ideas into concrete lumps of usefulness.

From these two limited points of evidence, I timidly suggest that although LW is pitched at generic rational folk, and contain lots of good ideas about rationality, the way things are written over-represent the novelty and importance of some of the ideas here, and may actively put off people who have good ideas about philosophy and rationality but treat them as "nothing big".

Another note - jumping straight into the articles helped neither of us, so it's probably a good idea to simplify navigation, as has already been mentioned, and make the "About" page more prominent, since that gives a good idea to someone new as to what actually happens on this site - something that is quite non-obvious.