My experience with HPMoR has been to find a story that is a) dementedly funny, b) loaded with a pile of mysteries to keep you wondering about crazy theories late at night, c) internally consistent and well narrated, d) useful for indirectly teaching people about rational techniques.

I was not aware of the number of rationalist novels circulating out there, and HPMoR was the first case I found of a fictional character explicitly defending my pet causes (empiricism, privileging experimentation, reductionism, atheism, the importance of SF in teaching creative thought). Among other effects, it naturally makes the reader want to know more about the author.