The odd thing about Alan Gowen (Gilgamesh, National Health) is that while he's extremely improvisational, his melodies can be quite simple and accessible (and rhythmic).

Here's guitarist Phil Miller playing "Arriving Twice" (the first 2:10 minutes of this video): https://youtu.be/RyK0vGUyQKc

And here's National Health with the same song--more complex in arrangement, but still the melody is the key: https://youtu.be/oRvvu2Gmrf4

In both cases, the performance is under two and a half minutes (the lengthy phrase is repeated once, and that's it).

A bit of bio: the National Health album is a "benefit" performance of Gowen's compositions put on by his former band mates because Gowen's wife didn't have the money for his funeral (Gowen died of leukemia at 43).