I don't think Chris is unlikeable, because you have to consider his situation. It's my opinion that he kind of numbs himself to everything after losing Kim, and after three years of that, it's easy to write her off as just a fling. Don't get me wrong, I don't like his actions all of the time, but I can understand them. I love MS because the characters are multi-faceted in that way.
As for Kim needing to be rescued, well, she's kind of in a situation where she has to be. Her only way of getting out of that life she's now leading is Chris. Even after they flee Vietnam, she's still stuck working as a bar girl in Thailand because she needs money. The only way she could have gotten out of it is by marrying Thuy, and who would want to marry the guy it is insinuated is responsible for the burning of her village? That, and she didn't love him.
Jimmy, what are you doing here in the middle of the night? It's almost 9 PM!