Contrast the old, pre-2003, Hastings-Japp-Lemon Poirot movies, with the New, Post-2003 Poirot style.
Nothing contrasts the different styles better then these slightly hyperbolized summaries:
The scene begins with Poirot and Hastings eating a dish prepared by Poirot himself. After they finish eating it, Poirot tells Hastings that it was made entirely from oysters, which causes Hastings to turn green in the face. Poirot, while accurately eating the square eggs, which miss Lemon purchased specially for him, admires the symmetry of the way Hastings' face turns green and says that he definitely understimated the order and method Hastings' organism was capable of. Then Japp comes in, and Poirot offers him some drink with a French name that includes many "oi"s. The mere mention of that drink causes Hastings to run away from the room, while hastily making some lame excuse. Japp tells Poirot about a murder or something like that, who cares anyway, and Poirot agrees to investigate, saying that his little grey cells need le exercise. The scene ends with Hastings lying sick on his bed, endlessly repeating "oysters... oysters....", while Miss Lemon sympathetically watches at him.
Then, Poirot goes about the murder scene, muttering something under his breath, but refusing anyone to tell what's going on. Meanwhile, Hastings is completely charmed by a nice lady who is somehow connected with the case. She is a bit drunk and tells him that it was she who did it all, but Hastings is so much in love with her, he looks sheepishly into her eyes, and doesn't hear a thing she's saying.
Finally, Poirot reveals the true killer - it's the 90-year-old invalid woman, who can really move around perfectly well. She played the part of the young lady Hastings was so in love with, because she knew that her private confession to Hastings will ensure that everyone will think that the murderer is a young lady, not an old woman.
Then we are subjected to a chase scene, with Japp and police chasing the killer, while she tries to escape. All the usual elements, like slow cars, snail-paced processions of schoolgirls, and subway doors are present. Finally, the killer is caught.
Final scene. Poirot offers both Hastings and Japp to dine with him, offering "the little grey cells of the oysters" to eat. Audience laughs as both quickly run out of the room with horrified expression on their faces. The end.
"Traditional" Poirot fans praise the episode as being "funny" and "true Christie", praising the performance of Hugh Fraser.
It is a dark and stormy night. A nun in a church, twisting a rosary, with a gloomy expression on her face, with lighting striking every moment, condemns a pair of homosexuals to Hell.That scene, touching on the issue of religious bigotry, is really deep and modern.The scene switches to Poirot receiving the news of the nun being murdered. Catholic Poirot is horrified.
Meanwhile, Lady Szantajevllska, a Polish aristocraut, prepares a special mixture of wax and goat blood. Also, we realize, that the church vicar's mother is kept in a mental institution. The vicar feels really horribly about it, and cries, while walking around that mental institution at night, in a very touching and deeply pshychological scene. Unfortunately, the vicar is murdered shortly afterwards.
On a night that is even more dark and stormy then the initial one, Poirot, very quickly, taking turns to SHOUT at every suspect, explains the solution - it was the vicar who had killed the nun, because he was furious she won't return his advances. (That theme is touching the relevant and actual Church corruption motive). But, haunted by his own guilt and his poor mother, the vicar had commited suicide.
"Traditional" Christie fans hate the adaption. Half the time they talk about it, they point out that the two homosexuals, Lady Szantajevllska, the nun and the vicar were not present in the original book. Other half they devote to complaining about the absence of Hastings (though he, too, wasn't in the original book). "Postmodern" admirers of Christie love the adaption, admiring its wonderful depth.