It's a musical that's based on the film Monty Python and the Holy Grail, which I've seen a few times. At the start, it stuck fairly closely to the film, so there were familiar discussions about migratory coconuts and the right of women in ponds to confer kingship. They were funny, but because I'm so familiar with them they just made me smile rather than laugh, and I wasn't really sure how it benefitted from being shifted to the stage. As the performance went along, it diverged a bit more from the film. For instance, they included the song "Always look on the bright side of life" (from Life of Brian), and removed some scenes from the film ("What's your favourite colour?").
They also added quite a bit of new content: in particular, there were several scenes that were more or less set in the present day (deliberately anachronistic). This went further as they poked at the fourth wall, e.g. a couple of songs where the lyrics basically said "This is the type of song that you get in a musical". Mitch Benn did something similar, and I enjoyed his version, but it didn't really work as well here; in fairness, Spamalot has been out for a few years, so I assume that they came up with the idea first. More generally, I think that a lot of that was aimed at an American audience, since the musical started on Broadway, and it felt a bit out of place here.
The cast did a good job; there were several understudies tonight, which didn't bother me, but it means that I can't comment on Sanjeev Bhaskar's performance. It was also impressive from a technical point of view: they did some imaginative things with the stage, and some very quick scene changes.
As people were leaving, they all seemed to be happy, and I heard a woman singing one of the songs. So, if you're a big Python fan then it's probably worth a trip, particularly since it will end on 3rd January.