Fowler is a complex protagonist; moreso than he initially seems. Complex enough that the things he does are unpredictable, though they always feel true to character. I mention this because while he's certainly used to represent the old colonial powers, he's still very much his own person. His struggle over getting involved in the end is fascinating, one of the few times I feel his emotions really come to the fore.
Pyle, of course, is not nearly so complex, though we see him through Fowler's eyes and so everything he does and says is tinged with Fowler's view of him as naive, an innocent. I'd be more inclined to doubt this view if not for the boat trip through hostile territory. And of course his meddling actions seeming to be inspired by nothing more thoughtful or deep than York Harding. One does feel sorry for him in the end--he's like a dog that doesn't understand why its nose is being smacked.
Phuong, as mentioned earlier in the thread, I never got a handle on. This is probably intentional, as she represents in some sense the Vietnamese themselves, never fully understood by the outside powers meddling with them. Fowler acknowledges this when he talks about how early on in their relationship, he would try to get her to really answer questions about what she thought or felt, until finally he had to give it up.
I enjoyed the prose a lot. Greene has a very smooth and readable style without sacrificing quality, and he has some great turns of phrase, alongside some recurring motifs. The relationships feel real, the story feels real... right up until the ending. When he receives the telegram that he's getting his divorce, it's just a step too far. He's got the girl, he got the order letting him stay, now he's got the divorce as well. At that point it just felt over the top towards a happy ending. I don't buy it.
Overall, a good read with plenty of character, somewhat marred by the finish.