Are you talking about the level of rationality, about the expected level (or types) of knowledge, or the grammar and sentence structure?

For obvious reasons, the level of rationality expected here is far higher than (AFAIK) anywhere else on the internet.

The expected knowledge at LW...is probably middling to above average for me. More relevantly, much more knowledge of science, and in particular the sciences that contribute to rationality (or, more realistically, the ones touched on in the sequences), which tend to be fairly 'hard'. I've found a much higher knowledge of, e.g. history, classical philosophy, politics/political science, and other 'softer' disciplines is expected elsewhere.

As for grammar, I'd say that LW is middling to below average, though this may be availability bias: LW is much larger than most of the other internet communities I belong to, so it could have a higher number of errors while still having a better average level of grammar.