Some quick internet research turned up Pierdomenico Baccalario as the author. Apparently, Scholastic is using a gimmick whereby Ulysses Moore, a key but unseen character, is the author of "manuscripts" discovered by Scholastic employee Michael Merryweather (whose emails to the Scholastic bigwigs begin each book). Oops, I'm blaming Scholastic, but I just checked, and the books were first published in Italy by Piemme, and list Ulysses Moore as the author, and Baccalario as the author. At any rate, it's a gimmick, but it's not intrusive, so I'll let it go.
This is an adventure/historical series for ages 8-12, and I thought it was really cute. I'll certainly buy the next one, since Isle of Masks, the fourth, ends on a huge cliffhanger.
Book 1: Door To Time: Twins Jason and Julia move into a mysterious house in Kilmore Cove, a tiny village in Cornwall formerly owned by the almost hermetical Ulysses Moore. Their parents (still alive, odd for the fantasy genre) leave them in the care of the house's caretaker, Nestor, while they finalize the move. The children make a new friend, Rick Banner, who comes to stay with them. The three children find a strange door and, after solving a series of puzzles and clues, they end up traveling back in time.
Book 2: The Long-Lost Map: Julia, Jason, and Rick are in ancient Egypt, but end up separated. Julia helps Nestor defend Argo Manor from Oblivia Newton, the woman who longs to control Argo Manor and its door to time, while Jason and Rick search ancient Egypt for a map of Kilmore Cove.
Book 3: The House of Mirrors: The children compete with Oblivia Newton to find the secret concealed in inventor Peter Dedalus's home.
Book 4: Isle of Masks: The children travel to 18th century Venice to learn the secret of the doors.
This series is really well-written, funny without relying on gross-out humor, splitting the difference between historical and contemporary settings. The puzzles are fun and add interest as the reader tries to solve the mystery along with the children. The children are engaging, squabbling but cooperative. The time frame is very tight: all four books happen over a couple of days. At the end of Book 4, the parents have come back home, so I wonder how Book 5 will work. Parents are such a nuisance to adventuring kids that most authors just kill them off. Books 1 and 3 have the children searching delightfully backwards Kilmore Cove, Cornwall, for clues. A rich supporting cast and ample secrets and mysteries make these fun. Book 2 has the children exploring ancient Egypt, with details and characters that bring the time and place to life. Book 4 takes place mainly in 18th century Venice with evocative sensory descriptions. The series is skewed a bit younger than Harry Potter (at least the later books), and I think any child who's a fan of puzzles, historical books, and/or fantasy will have a blast reading them. I look forward to seeing what's in store next.