I'm another one who likes both. The Swedish versions can't be more faithful to the books, at least in storyline terms if not spirit, as with the exception of the first one, 'Before The Frost', they're not adaptations but original stories. The first series in particular was excellent though- apart from Krister Henriksson, Johanna Sällström was if anything even better as Linda (a match for Branagh in sheer intensity), and the supporting cast were all good too. The second series I think lost something- apart from the tragic suicide of Johanna, Ola Rapace as Stefan had also been written out (just when they'd made the character really interesting), and the scripts were a bit more 'generic cop show'. They also seemed to soften the character of Wallander a bit- though Jussi the dog was very handsome, I'm not sure Kurt's a dog person....
I've recently started working my way through the novels, and having read 'Faceless Killers' and 'The White Lioness' I think Branagh's portrayal is more accurate. Wallander is a deeply flawed, troubled man, and that really comes through. Ken's mispronunciation of his own character's surname (when pretty much everything else about the series has superb attention to detail) is a little irritating though. There's nothing confirmed about a third series AFAIK, I hope they keep going for a few years......