It's the fourth Tintin book and the first one that's not rubbish. (Herge disagreed only slightly, regarding #5 as his first good one. He also redrew this in 1955, as he'd already done with all the other black-and-white Tintins.) It's got a plot, instead of just a string of set pieces. Herge was starting to work out where he was going with this series.
In short, it's a transitional work. This makes it quite interesting. There are ways in which this book is better than normal for Tintin.
Firstly, this is Tintin without his gang. Captain Haddock, Professor Calculus and Bianca Castafiore don't exist yet, despite the English translators adding a reference to Marlinspike on p1. Thompson and Thomson make their debut, admittedly, but here they're capable of being ingenious and competent. They're save Tintin from a firing squad and Snowy from ritual sacrifice. They wear effective disguises. They're still stupid, but not absurdly so.
Also, Herge's working harder on their dialogue than usual. The meaning-manglings in their "to be precise" corrections are quite witty.
Tintin's adventuring solo, unless you count his dog. This is interesting for its effect on Tintin's characterisation. He has some! In other books, he's the kind of transparent everyman you'll see in many Japanese harem anime and isekai light novels. (Herge's reasons are different, but the outcome is similar.) Here, though, he's not yet merely a straight man for Haddock and the others, so he gets some hints of personality from time to time. He gets cross. He shouts at annoying people. He even gets to be a gullible idiot for comedy on p13. "Just as well I didn't fall for his patter. You end up with all sorts of useless junk if you're not careful."
Sometimes, he's even cool. I love the tiger straitjacket scene, although I'm mildly disappointed in the fun scene of how he deals with a comedy masked evil organisation. The gang learn that they've been infiltrated, but they have a rule against taking off your hood. One of their number starts shouting and threatening, demanding passwords and eventually ordering the others to visit him one by one in a side room. When we eventually go through, though, we see the baddies all tied up. Tintin's been knocking them unconscious as they come through, so does that mean Tintin was Mr Shouty all along? Alas, no. "I must say I was lucky to have been called first!"
The title and cover are misleading. You'd expect this to be an Egyptian story, but Tintin only spends five pages there. There's also the Middle East, India and various ships, planes and boats.
The book usually feels realistic, with good visual portrayals of its different countries, but it's not afraid to be childish. Fat people can be used as trampolines. Animals have a common language, letting Snowy the dog talk to an Indian sacred cow. (When Tintin manages to talk Elephant with the help of a trumpet, could he therefore have used this to talk to Snowy?)
It's not a bad adventure. You can see the seeds of later Tintin books, e.g. Professor Sarcophagus being a proto-Calculus. Herge's framing, composition and action scenes all remain dead, but his ligne claire style is easy to read and a good fit for a travelogue. The desert fort on p31 and the Indian parade on p61 are both particularly attractive. This book has a sequel, The Blue Lotus, incidentally, and I'm looking forward to it.