So, I wasn't really the target audience, but it actually turned out to be a lot of fun, so I enjoyed it a lot more than I'd expected to. The children in the audience seemed to enjoy it too, although I think that some of the younger ones (e.g. the two year olds) didn't really have enough of an attention span for it. If you are planning to take your kids to a panto, I certainly recommend this one, although it finishes today (Sat 5th), so this advice would probably have been more useful if I'd posted it earlier.
Minor spoilers follow...
This show definitely had the things you expect from a panto, e.g. a principal boy played by a woman with plenty of thigh-slapping. (I'd be hard pressed to explain exactly why that's important; It Just Is.) Another traditional element was the pantomime horse, or in this case the cow. I hadn't really thought about this before, but it occurred to me that this is an underrated skill, particularly for the person doing the back half. It can't be comfortable to spend so long bending over, and presumably they can't see much of what's going on, but they still have to move in time, respond to cues, etc. So, thumbs up to the duo who handled that role.
Speaking of underrated skills, I was also very impressed by the backstage crew, since they pulled off some very quick set changes. They came up with an interesting way to show the beanstalk rising, which was almost abstract: there was a completely black stage, with leaves and things flying around. At first I thought that this was done with wires, but then I realised that there were people dressed like ninjas moving these objects around. However, it was damn near perfect: I only caught a glimpse of the people twice, and that was when I was specifically looking for them, so they were almost invisible.
In a way, this was almost a musical, with some pretty catchy songs. (As a minor criticism, the music was a bit too loud in places, drowning out the voices.) The one that particularly stuck in my mind was "Danger Men At Work". It's hard to describe, but I'd be happy to sing (croak) it for you in person if you ask nicely. The basic idea is to keep repeating those four words (five syllables), but some lines of the tune ("Knees up Mother Brown") only have four notes, so you wind up singing things like "-ger Men At Work Dane", and the challenge is to sing one phoneme while thinking about a different one. I think that would work quite well as a party/drinking game, or as a campfire song, and it's kept me entertained on a few of my cycle journeys.
As I mentioned, Amy played Barbie, who is obviously an addition to the traditional cast. On the other hand, looking at the posters I've seen for celebrity pantos, I think she fitted in a lot better than the Crazy Frog or Sooty and Sweep. Actually, this reminded me of something I heard about Frasier: the writers said that they had to tone his character down a bit from Cheers since he was the lead role, so Niels was the one who could go to excesses (e.g. dusting his seat before he sat down). In a similar way, while Jack was the nominal hero, saying dramatic things like "I'll deal with the giant! I'll find a flying machine, and go up to the clouds!", this allowed Barbie to offer a sarcastic commentary, with quite eloquent hand gestures.
When people talk about Pixar films, the general concensus is that they offer something for adults as well as children. That's a useful goal in a panto, since there will be a mixture of age groups in the audience. There were a few jokes which involved slightly risque puns, e.g. "Can I feel your baps?", but they didn't really appeal to me. A better example came during the slapstick scene, which involved building a box. This was done in the style of Laurel and Hardy, with the classic example of anaphora resolution. ("When I nod my head, you hit it." "Right!") This was probably new to the kids, so it worked purely at face value. However, Barbie was able to add something to the scene, by turning away and covering her eyes in recognition of the inevitable; the youngsters probably wouldn't pick up on it, but adults would. Mind you, I think it's slightly unfair that I got soaking wet (in the audience) while Barbie (on stage) stayed completely dry!
One slight drawback to audience participation is that the audience might not do what they're supposed to. For instance, at one point the main villain (Fleshcreep) sets the scene by describing the cloud kingdom (where the giant lives). This was all done in rhyme, so I don't recall the exact words, but it he said something like "The giant is the absolute ruler". At this point, things went slightly awry.
Voices from the audience: "Oh no he isn't!"
Fleshcreep: "Yes, really, he is!"
Audience: "Oh no he isn't!"
Fleshcreep: "Please agree that he is, or we'll be here all night!"
A bit later, there was the traditional back and forth, and he then said to the audience "Right, this is the bit where you say that!" So, I guess that's something to be careful of when you write a pantomime: try to avoid things that the audience might latch onto by mistake.
(Of course, I don't have a perfect track record at this: I've previously described my trip to see Pinocchio as a child.)
On the plus side, I was particularly impressed by the guy playing the Dame: he did an excellent job of thinking on his feet, and improvising to deal with the unexpected.
As an aside, I briefly met the guys who played Fleshcreep and the Dame after the performance, but I didn't recognise either of them without the costume/make-up! Speaking of make-up, I did notice a slight resemblance between Fleshcreep and a Wraith (from Stargate Atlantis), i.e. diagonal "cuts" under the eyes; I'm not sure whether that was deliberate. The only minor problem I noticed was near the end, when Fleshcreep lifted his arms in the air, so his sleeves fell back and the green make-up didn't quite extend far enough past his wrists. Still, that's easy enough to resolve, so they probably corrected it in subsequent performances.
One other interesting thing about this performance was that they put some thought into the plot. In the comic Fables, there's a scene where Jack (now an adult) is trying to con someone out of money. He claimed that he still had the other four magic beans, since only one had formed the beanstalk, which led to the following exchange:
"They're very rare, and I bought the only five of them left."
"How rare could they be if they were selling at the rate of five beans per cow?"
In the panto, they got round this by saying that a fairy had deliberately chosen Jack as her champion: since she wasn't allowed to directly intervene, this was her way of nudging events in the right direction.
So, it was definitely worth the trip, and I may well go back next year for their next production.