I was a huge fan of A Series of Unfortunate Events, and all I really wanted from Who Could That be at This Hour? was more of the same. It is, after all, connected, being a prequel that chronicles Lemony's early adventures as an investigator. Certain trademarks of the series are gone (the many, many warnings to not read any further, for example) but it's still very much the same voice. If memory serves, the reading level is a bit higher than ASOUE, too. And you likely wouldn't have to read ASOUE to understand the events of this new series. But seriously, why wouldn't you?
I don't really have anything to complain about (which makes this a tough review for me to write). I love Lemony's style, and it's spot-on here. I like that it's disconnected enough to allow first-time readers and those not caught up on their Lemony lore to follow what's going on, but still obviously part of the same strange universe. And the ongoing theme of the wrong question being asked at the wrong time is used just enough that it doesn't become repetitive and gimmicky. There's a cliffhanger, but it's still an end to this book, while still leaving a lot of interesting questions open. My only real complaint is that I can't immediately pick up book two.