Pleasant. Not a bad thing at all, in my view. All of the Amelia Peabody novels are pleasant and that is sometimes all that one wants. This book was quite gripping too. It also had the advantage of taking a step back in time to when the Emerson 'clan' was not as large. It felt like that created fewer distractions and added depth to the characterisation.
Many crime novels, particularly when the series runs to so many books, can seem a bit formulaic, but that seems to matter less with the Amelia Peabody books than with others. The writing is excellent and very entertaining, as ever.
Ultimately, it may boil down to a matter of expectations. If you want to relax, have a grin and learn a bit along the way, then please choose this book. If one is after a historical tour-de-force, then perhaps 'Crime' isn't the right category to be looking in.
By the way, I would love there to be a book in which Emerson is left to his own devices. It could be a little too close to home, mind you.