Gabriel was not a good guy that's for sure, but he had a way of mocking situations and people, making snide comments, always ready to take amusement at someone else's expense, and when he did this with someone like Gerard, it was such fun to watch.
Setting his "not-so-good-deeds" aside however, I felt bad for him. He never got along well with his father, and there's a scene with him and Daniel that is so very well done and sad, with [spoiler]Gabriel begging to know why his father never loved him as he so obviously did Quentin. Daniel seemed incapable of loving Gabriel due to his disability, quite a shame really! Gabriel wanted and needed his father's approval, and perhaps if he would have been accepted as a child by his father, he wouldn't have grown up to be so bitter.[/spoiler] I'm not making excuses for him, just trying to comprehend his actions and motives.
Edith was also very cruel to him, taunting him, making him feel worthless because he couldn't walk, [spoiler]even though he was playing that role falsely, she didn't know that, and first time viewers didn't know that.[/spoiler] She should have accepted him as he was, yet another incident where he was scorned by someone who is supposed to care for him. Granted, we don't know under what circumstances they were married, perhaps they were forced in to it, and that might explain her coldness, but I still felt bad every time she was cruel to him.
Did he have faults? most definitely! But in some ways he's a tragic man as well.
I also liked Cyrus Longworth. He was a gentle man who was trying hard to make a difference in the world, [spoiler]and in the end he came to such a sad fate.[/spoiler]