Firsts things first, I've not read the books, so keep that in mind...
I'm just back from seeing it and I LOOOOOOOVED it.
I have to agree with what others have said already.
The main thing I noticed was how refereshing it was to see a film of this type without all the typical forced hollywood things to try and widen the audiance, hopefully it will be successful and open up more support for this type of film being made in Europe. This film is made for people who like action/adventure and paranormal/fantasy stuff it doesn't try to shoehorn in love interests, eyecandy or anything like that, it just tells its story and tells it well.
The only negative I can possibly think of is that an hour and three quarters wasn't enough, I could easily have watch 5+ hours of it, the demonic monsters were fantastic and I would have loved seeing them get more or longer scenes.
The fight scenes were brutal and the film pulled very few punches in regards to violence, but it rarely felt excessive. The plot stumbled a little a few times, and at one point things felt a little rushed, but they still managed to fit in just the right amount of characterisation.
That's another thing that having a longer run time would have helped with, I don't know if the plot stumbled per say, from my point of view at least, but some more scenes could easily have kept the pacing smoother. I guess at the end of the day this doesn't have the big name, fanbase, or known cast of Lord of the Rings so having the film run for two and a half or three hours would be seen as too much of a risk.
I think the thing that made the violence seem so brutal and yet not excessive was how realistic it was. The weapons weren't like light sabers slicing off heads and limbs all over the place in massive gouts of blood with no effort at all on the part of the bearer. So there was blood, but a lot less than you would normaly expect in a movie of this sort, a more realistic level, while they also made great use of "just out of shot" deaths.
The fight choreography was stunning, the varied styles that come with different levels of training and different weapons showed in every fight.
Really I could go on and on about how much I liked this, and I went in expecting a lot from it.
Did it convey the early 17th century? not sure, but was very atmospheric and you didn't need telling it was in England as it it was either snowing or raining in most of the film 
I'm not really sure it conveyed the early 17th century either, but certainly it was a good alternate version of "yee olde days" which I guess is what they were aiming for.
I didn't need to be told it was England because it was full of witches, sorcerers and evil thugs.
