I don't specifically have a problem with Denna. I do however find Kvote's overboard infatuation with her irritating. But I guess the portrayal is pretty realistic. You do get people who have a 'hero' complex always falling for someone that they feel they could save in some way or the other. I guess Kvote feels that way because he couldn't do anything to save his parents. Though those type of relationships rarely ends happily for both parties. (I also have the feeling that Kvote's "hero complex" is supposed to show as opposed to his Kote the bartended character.)
I'm about 3/5 of the way through, and this is largely my thoughts.