I think the Dante Club was quite good. It gets a bit predictable, but the ending really throws you off. Besides, if you read la Divina Commedia, you'll really appreciate all the references and the thousand meanings behind each phrase
it is quite gruesome, but Dante's Inferno wasn't a walk in the park either
What I found most appealing is that the heroes are actually anti-heroes. They're not cops, just learned old men. They can't go running after a crazy killer, but they still fight with their own weapons.