I recently discovered Simon Green's Ishmael Jones series and have enjoyed it quite a bit. Briefly, Ishmael Jones and his partner Penny work for a mysterious Organization solving paranormal mysteries. Murder is always involved. The plotting of the murders is generally the weakest part of the books, and "House on Widow's Hill" is no exception to this rule; however, the characters and dialogue are great fun and the series as a whole has a slightly old-fashioned feel to it that I like. It's an update of the locked-room mystery genre.
The mystery behind the mystery (i.e., what the heck is going on in the house being investigated) is intriguing and there are some really chilling developments that the ghost-hunting team has to confront. Ishmael and Penny get more character development and I'm starting to wonder just how much the Organization knows about Ishmael's background... probably more than he thinks.
There are weaknesses in the series, as reviewers have noted in the past - but if you just go along for the ride I think you'll enjoy the books, and this one in particular is very good.