I've been a big fan of Kenneth Branagh's Wallander since Season 1. I'm not familiar with Henning Mankell's books yet (they are in my future plans) so I can't really comment on this has an adaptation but I love Branagh's portrayal of a middle aged Swedish detective who feels keenly the burden of having to investigate the darker aspects of human nature and who is completely devoted to his work.
Branagh's Wallander (there are also Swedish films about the same character) isn't so much hardened as left exhausted by what he sees. I particularly like the slow paced action that gives us time to appreciate the landscape, the setting, the colours... Unlike other police procedurals where characters seem to be running one way or the other, in Wallander there's time to think about the crimes, to investigate and put two and two together and for those tidbits of family or social life that make it even more real... I does help that the episodes are almost two hour long, it gives the scriptwriters time to develop the action and the viewer more time of good drama.
Despite the violent murders shown, that part of Sweden seems very nice for a holiday. The landscapes are beautiful and I loved the house Wallander lived in during this third season. One of the episodes takes us to Latvia which was an interesting change of scenery. My only complaint is that each season only has three episodes and while quality is better than quantity I wouldn't have minded to have both. I'm very happy that they decided to do a fourth season!