I loved this final boss. Stranger/Campman was exactly the right boss for Walking Dead--another human who has had to survive, and been warped by the sheer hopelessness of his situation which your party was at least partly responsible for. As soon as I saw that car sitting in front of the Marsh House, it sent a chill down my spine. What a moment. I knew who was waiting for me as soon as I saw it, and for some reason, it only strengthened my resolve to kill him for what he had done to us. Kenny and Ben, both of whom I had just barely come to like and respect, were killed because of this man. No matter whose fault it was that he had Clementine, he indirectly murdered my closest friends, and had to pay. The final confrontation was just as tense and riveting as the series deserved, and I'm glad they used the person they did.
I think he's the best boss for ALL the reasons people mention not liking him, it makes perfect sense. A man whose life was ruined by Lee (optionally) and his group (mandatory) is trying to justify his reasons to kill Lee, but it's hard because he sees exactly how motivated and good Lee is, and is resorting to every bad thing he can to justify Lee's death. PS: I also liked how anti-climactic it seemed, you get the hyped up big bad enemy of the entire series since the end of episode 3 in your hands, and he's just a broken down shell of a man who faces Lee and the player's anger.