Well, it had potential
I don't think Penny Dreadful is necessarily God-awful, and the suspense can be quite strong (at least in the first half), but boy, does the thin story drag on for quite a while. The central performances were okay (though some of the characters can get a bit annoying quick), and again, the first half was strong, but after awhile, the material just got pulled too thin.
For a random movie to spend a night with, you could do a lot worse, but I find it difficult to believe there's many people out there who would throw this on their "Favorites of the 2000's" list. Not terrible, but I think it's a bit below average.