Amy and Dan became unbearably catty in book 3, but in this one they bond more as you would expect two orphans in a life-threatening situation to do.
The Egyptian aspect was great fun as well. I actually learned a few things. And
There is plenty of fun historical name-dropping. Napoleon, Churchill, Mark Twain, Howard Carter and many more show up in one form or another in the course of this book. If nothing else, kids reading it are getting a good amount of fun history with their adventure.
At this point I don't really care what this is all leading up too. I just want to read them all so I can talk to the kids that are into them. Every character is either completely self-centered and will screw over the kids (I can't believe they keep falling for that) or are really good and will probably die before the end of the series.
*Update: Okay, you can see why I thought Jude was a male. The only other Jude that pops to mind is Jude Law. And Star Wars books? C'mon. It was an honest mistake...