I really enjoyed it and was gripped from start to finish. Be warned though, it is very very dark. If you are put off by the first episode then follow your instinct and stop watching. It doesn't get any lighter, although that's not to say it's without humour.
If you're not put off then you'll be rewarded by some fine acting particularly from Tim Roth and a plot that slowly and dramatically unfolds. Just go with it. The scenery is genuinely awesome too.