Season 1 was great. Season 2 was good, a bit more messy.
Season 3 was a complete failure: Casting issues, awful acting (or lack of direction?), dumb writing and even dumber directing. The Story had no sense at all, the character's actions had no sense, it was just a mess. I kept watching just because of Tim Roth.
I'm always frustrated when they decide to cancel a series, but it's even more frustrating to renew a series for a last season with a change of direction, many different writters and a total lack of artistic and clever sense, especially the finale episode (remember the Name: Alice Troughton! I'll try to avoid your work as much as possible, you're awful! Shame on you to make such a finale episode! So disappointing!)
Season 1 is 9/10
Season 2 is 8/10
Season 3 is 2/10