The main virtue of "Death on the Nile" is Agatha Christie's unbeatable whodunit plot, which is arguably even more beautifully constructed than that of "Murder on the Orient Express." The latter had been adapted for the screen in 1974 by one of America's great filmmakers, Sidney Lumet.
Like its predecessor, "Death on the Nile" was filmed with a fine all-star cast, in which Peter Ustinov, Bette Davis, Mia Farrow and Jack Warden stand out. Ustinov's Hercule Poirot is perhaps a bit less eccentric than Albert Finney's or David Suchet's, but I actually like all three interpretations.
The film is as lavishly produced as "Orient Express." It has nice costumes and beautiful natural locations. John Guillermin isn't as strong a director as Lumet is. Consequently, the images in "Death on the Nile" are pretty, but less artistically interesting than those in the preceding film. Moreover, Guillermin's visual storytelling is a bit repetitive (he shows all the possible versions of the murder in detail, which tends to become a bit tedious after a while), and the first half could have been shortened a bit. Still, the direction is way above average, and Guillermin handles the action scenes and the solution in a convincing way.
To me, "Murder on the Orient Express" is the most artistically satisfying Poirot film, but "Death on the Nile" is the most entertaining of the Poirot adaptations with Ustinov as the Belgian detective. "Evil Under the Sun" is also enjoyable, since its strong second half more than compensates for the overlong exposition.
I'd give "Death on the Nile" a rating of *** out of ****.