He's also extremely judgmental against mages, and I find the whole "forbidden love" trope that Fenrismancers adore while romancing him as a mage to be extremely childish.
Rivalmanced Fenris (Fenrismancers, no flame, we have diferent tastes) and he screwed up some of the quests, dumped her after 1st night (I did not know he returns in Act III, but whatever) and FORCED her to challenge Arishok.
Also, if you romanced Fenris and then left Hawke in the Fade, there could be some really great opprotunities for Bioware to twist that knife into the hearts of Fenrismancers everywhere.