Reger is a bit bipolar, his more contrapuntal music (e.g. the organ works, or the fugues in the two big variation sets for piano) tends to also be extremely melodramatic whereas some of his other music exists in a state of constant chromatic haze that prevents any real tension from developing (e.g. the violin concerto, which is probably my favourite of his pieces, and will appeal to anyone who likes the Elgar concerto but wishes it had less stuff happening and fewer melodies and less excitement*). Like Szymanowski it's very much an acquired taste. The pieces I'd recommend as introductions to Reger and his style would actually be the four Sonatinas for piano, op. 89—if you don't like them, you probably won't like any of his stuff.
* I do like it better than the Elgar concerto but I have specific manias when it comes to music