I think another problem people have with Fenris is his stance towards mages. He clearly does not trust them, and for some people, his attitude is horrible. It doesn't help that he's rude to popular characters like Anders and Merrill. If that is their favorite character to romance, then having Fenris say the things he does won't make him look very good. Admittedly, there are times where I wish I could have Hawke turn around and smack Fenris, but I always let it go.
Also, I think that there are some people that are still confused about the friend/rivalry system. They seem to be under the impression that if you have high rivalry (not very difficult if you're supporting the mages and take Fen everywhere) then he hates you. Not once have I seen evidence that would allow me to reach that conclusion, but we all view things differently.
People might not take him many places if they want to play their game with the 'ideal' party, so his rivalry/friendship bar might remain in the neutral range and you never get any of his Questioning Belief quests. Then in the end, if you side the mages, he'll refuse to help. Not endearing to a lot of people.
Of course there are some that might have decided from the beginning that they weren't going to like him, and nothing anyone can say will change their minds.
The same thing goes for Isabela, or any of the characters really. People see their dominate trait (For Fenris, apparently its his dislike of magic; Isabela its her 'wanton ways') and if they don't like it, they don't like the character. Frankly, I find that to be really stupid. To me, seeing all the hate for Fenris or Isabela makes me think that people don't really get it. I have seen posts on here where people say that they don't like Fenris, so they give him back to Danarius every time.
This is where I run into problems. I'm sorry, but if you hate a character
that much, that you are going to give him back to a known blood mage (one who inflicted enough pain on him that he no longer remembers the first part of his life as a slave) then you need some help. I don't care what type of Hawke you are playing as, that is a douche move. This ex-slave came to you for help and has offered to help you with anything you needed from the beginning. Yes, he does not like magic, but after the life he has led, can you really blame him? Tell me how you would act after being in the same exact circumstances as him, because I want to know. Most of us have seen the letter you get if you return Fenris to Danarius. It blows my mind to think that someone hates him that much that they will let him have his memory wiped again. It isn't even worth it finacially at that point in the game, so I don't want to hear the excuse about getting gold for doing so.
*gets off soapbox*
To people that do not like certain characters, all I have left to say is if they bother you that much, then don't recruit them. That way, you don't ever have to put up with them. And if that character is Fenris, fine. I will be more than happy to play a walkthrough where I recruit him for every time you don't.
Well, now that fI've finished my mini rant for the day, I think its time for me to head to church and pray for those who don't think Fenris isn't a worthy character to get to know. Alas, if only there were someone like Sebastian to keep me company at church