Script versus short story
Exton's script is largely faithful to the source material, but he makes several additions and some changes. That's not surprising, considering that the short story is shorter than most. First, he adds a subplot in which Hastings is considering buying an Italian race car from two Italians, Mr. Vizzini and Miss Fabbri. This provides some comic relief and character development (Hastings and cars), and a rather brilliant wedding scene (The Godfather style). It also ties in with Signor Ascanio, since Vizzini is the one who has been a victim of blackmail. Second, Exton adds a subplot concerning Miss Lemon. She is seeing Mr. Graves, Count Foscatini's man servant (he pretends to be a private secretary). Slightly out of character (both Christie version and the TV version), but certainly an amusing addition - and a nice way to incorporate Miss Lemon. It also provides an important clue (Graves has a boat in Chichester called 'Fantasia Felice'). Third, Japp replaces the unknown local inspector. A sensible change, in light of his position in the series by now. Fourth, a subplot on the Italian government is added (Graves tells Poirot that the papers are a matter of national security), including a scene at the Italian embassy and a somewhat unbelievable embassy secretary (would he really reveal everything to Poirot?). Finally, there's an added chase scene (as always!) - the most obvious time filler I've seen so far in the series. All in all, though, this is an entertaining adaptation, and if you accept the changes, it remains faithful to the plot essentials.
Directing, production design, locations, soundtrack
Farnham's direction is competent, and he makes good use of the locations and sets. The production design, particularly in that wedding scene, is extraordinary. Locations include Avis Rent-a-Car, 8 Balderton Street in London (the garage), the roof garden in Kensington High Street (the wedding), Addisland Court (Count Foscatini's flat - also used as Carlotta Adams's flat in Lord Edgware Dies), Jenkins Hotel (where Ascanio is staying), Bosham, West Sussex (used as Chichester). Gunning's soundtrack is particularly nice, with several Italian undertones. Sadly, it has not been released.
Characters and actors
As I've already mentioned, there is character development for both Hastings and Miss Lemon in this episode, and it's quite nicely done, too. I even like the joke about the cats at the end. The guest actors all do a decent job, but the two 'Italians', Vizzini (David Neal) and Fabbri (Anna Mazzotti) are the ones I remember.