MusicalCriticism.com has a good review of Candide and seems happy with Alex: "Thank goodness for the sensational, suave Alex Jennings: he's perhaps the only person completely at home and relaxed with the material, which is miraculous given the challenge of the triple role he plays. As Voltaire, he draws the audience in with his ironic declamations; as Pangloss, he plays the bogus teacher to a tee; and his portrayal of Martin's deep cynicism is one of the most touching moments of the evening. His singing and diction are just right for the piece, and, in a way, it's worth going just to see him."
They also have the first picture!
Full review: Musical Criticism
More mixed feelings about the production from Edward Seckerson in The Independent, but again only praise for Alex: "It was Bernstein and Hellman’s idea that Candide’s tutor, the philosopher Dr. Pangloss, should, as a re-embodiment of Voltaire, become our master of ceremonies. Subsequent rewrites have made this more explicit and here we have the brilliant Alex Jennings slipping nonchalantly between the two – not to mention Pangloss’s alter ego, the cynic Martin, whose belief in “the worst of all possible worlds” achieves greater resonance in this production with his bitter laughing song “Words, Words, Words”. Jennings nails that."
Full review: The Independent