That opening is a tight, focused piece of storytelling. It's also part of a narrative (effectively the Trojan War and Odysseus's return) which provides Fry with a coherent dramatic shape. As a result, although Part 3 doesn't manage to maintain the high standard of the opening throughout it is more satisfying than the other two segments. The problems elsewhere arise from several factors.
It is fair to say that in both Part 1 (Gods) and Part 2 (Heroes) Fry attempts to provide a similar focus - first around the creation of the pantheon of the Immortals, secondly around the adventures of Heracles. But neither of these works as well as the Trojan War and its aftermath - the earlier stories are too episodic, they don't I think have the same capacity of emotional engagement as the plight of Odysseus - forced to war through his own cleverness, then condemned to ten years of wandering. Then there's the problem that Fry chooses not to simply tell the stories. He knows an awful lot of classics, and he's anxious to share this knowledge. He also wants to tell us about his own attachment to these stories, and to explain why they are still relevant to us now. These digressions can be interesting/amusing but overall they mean that this epic has a theatrically unsatisfying lecturing tendency, and we digress too often (and over the three parts repetitively) into the byways of Fry's life and classical civilisation through an increasingly tiresome device called Mythical Pursuits. In the first two parts these elements serve to heighten the episodic nature of the stories. In Part 3 they are an unnecessary disruption of Odysseus's story. Finally, Fry includes a section at the start of the second half where the audience can e-mail in their questions - some of these afford further excuses for yet more digressions, some allow for quite funny one-liners, and one simply became a self-publicity opportunity for Fry's books which led me to contemplate whether what we were witnessing was verging on an advanced kind of book tour.
One of my interests in seeing these shows was curiosity as to what Fry would be like as live performer. He's certainly a warm presence, and he can tell a story well, often grippingly. But I have seen more gripping stage performances - shows in which you really can't take your eyes off the performer - Fry is not in that league.
I suspect that the less you know these stories the more you'll probably enjoy Fry's versions of them, but I'm afraid for me comparisons kept swimming around my brain - and two in particular. When I was growing up Tony Robinson retold the Odysseus narrative as a series of 1 person episodes for BBC Children's Television - filmed, as I recall, in appropriate locations. His delivery (annoyingly I was unable to find any segments accessible on-line to check my memory against) had a dramatic urgency that Fry with his slower pacing doesn't seek. His modernising updates had a gentler humour but also felt less forced than some of Fry's one-liners - I recall a running gag about Odysseus's men playing cricket. The other was an extraordinary trilogy of radio plays for BBC Radio 3 maybe 15 years ago now by Andrew Rissik which explored episodes of the Troy story. Rissik's writing has a poetry which Fry's lacks (all Fry's heroes tend to be described rather similarly), he put the listener inside the minds of individuals more consistently and successfully than Fry, and although we only encounter one God (a weary Hermes) he has a mystery and a disturbing power to him which, to me, was somehow more effective than Fry's multitude of often comedically accented immortals.
The show also posed for me a further question. It is going on a limited UK tour. Did it need EIF backing to come to the city or, like some other elements in recent programming, could it have reached Edinburgh as part of the regular year's cultural offer?
There were finely done segments to these shows, and Fry is nearly always an appealing performer, but it doesn't justify the epic length. If you are thinking about catching part of this in London or elsewhere I recommend Part 3.