This show definitely does not deserve a 5.9 rating (at of the time of writing this review). The acting is perfectly good, the cinematography looks nice, the plot is interesting and the characters are likable and not too one-note. Overall, it's a very competent show.
As several people have said, it's a very original idea for a plot too. I mean, the seedy side of the art-collecting world isn't something you see on TV very often. Also, I really like how they open most episodes with a little 'history' on the pieces featured in the episode -- adds a nice amount of flavour to the show.
I enjoyed season 1 immensely, and I'm looking forward to season 2. Too bad it didn't go on for longer. All in all, this show might not be a groundbreaking masterpiece, but it's also no 5.9.