Ahtisaari won the Nobel prize. I have written previously about him and I won't repeat that. Here is a good article about his "result-oriented" style of negotiating.
I think that this result-oriented style has been his undoing in Kosovo. His main strength is that he is well-connected in international diplomacy and is in a position to assure himself of support from the main powers in the world. But this diplomatic orientation has a price in that those powers may pose their own demands. In the case of Namibia and Atjeh this didn't provide problems as those countries weren't very interested in the subject. In the case of Kosovo because of the Kosovo War some countries were more or less parties in the conflict and as consequence very partial pro-Albanian.
In previous conflicts Ahtisaari had had a very open style of negotiation. "nothing is decided until everything is decided" was one of his slogans to discourage the parties from claiming partial victories in the negotiations. This flexibility was absent in his Kosovo negotiations where he immediately went to Belgrade to tell Serbia that it wouldn't get control back over Kosovo and could only negotiate about minority rights for Kosovo's Serbs.
It looks like in Kosovo Ahtisaari had become somewhat lazy after his earlier diplomatic successes. I saw him in a meeting answering questions and I got the strong impression that he had never really studied the position of Kosovo's Serbs. His proposals for autonomy totally ignored the specific problem of refugees who hadn't been able to return for many years and the continuing unsafety.