If the self genre is already experimental, which makes it very eclectic and ample, the styles inside of it are the same way very numerous. Thus it's pretty hard to talk of styles indeed. I'd say it's more appropriate to talk of tendencies (influences and moods) than of styles, because, I repeat here what was said on the first faq, the style will rather concern the artists isolatedly considered than the whole genre. Even so, to make the understanding easier, we can try to bring up some categorization of the artists according to the influences/mood, gathering them together into groups. I'd set these as the main influences/moods on the genre: hip-hoppy, trip-hop-rock, jazzy, dark, depressive (melancholic), happy / pop, minimal, instrumental.

On the dark angle, there are bands such as Portishead, U-topia, Sunday Munich and Sin; more pointed to a depressive/melancholic mood we can name Canidas and Antenne. Smoke City, Si*Se and Heed  are examples of a happier mood, and Morcheeba and Laika infuse it into a poppish vibe. With rock influences there are artists as Lunascape, Earthphish, Monk & Canatella and Puracane; of hip-hop, Tricky, DJ Vadim, Kid Koala and Archive (on the album Londinium); of jazz, Portishead (yes, frequently a band will have more than one strong characteristic), Wax Poetic and Aria (who's also very influenced by hip-hop). On the instrumental side, there are artists as DJ Shadow, Pelican City, Bonobo, Rekhmire; generally we'll find more of downtempo than of trip-hop when we consider instrumental downbeat. On minimal music, we can name artists as Canidas and Pomegranate.

There are also some characteristics which are peculiar to certain artists, as the influence of bossa nova on Smoke City, The Boyz from Brazil and Thievery Corporation; of tango on Gotan Project; of flamenco on Federico Aubele; of indie rock on Bowery Electric; of 60s music on Goldfrapp; of drum n' bass on Baxter; of electro on Andrea Parker; of trance on Olive and Balligomingo; of Arabian music on Nitin Sawhney and Soap Kills, of Jewish music on Oi Va Voi. There are yet artists who work a lot on the electronic and abstract side of the songs, creating a very urban atmosphere, such as Microbunny and Bowery Electric.

The preponderance of a mood/style does not eliminate the others (generally there is a combination of many elements to the creation of the atmosphere). Artists which bare reference more to dark trip-hop can sound sometimes, for example, happier. Portishead, even being preponderantly dark, can sound depressive sometimes; and this way things go... In fact, there are no pre-made formulas, no rules.