It was series three that made the Man from UNCLE lose popularity, supposedly because of the introduction of high-camp elements, which, as I have noted here before, were actually there from the beginning in my humble opinion. One of the things I find interesting about this episode is that the opening scene is so visually derivative of The Avengers: the step ladders reminiscent of Mother's only-used-once office, & the red phone box. It is rather a misdirection because (to my eyes) it leads to the wrong impression.
However I personally am not disappointed by the rest of it. I *love* the idea of Thrush operating from a theatre. I love it, I can't describe how much I love that idea. It's almost a parody of UNCLE operating out of a tailor's shop, & shows which parody themselves have to be careful how they do it.
I can see where it went wrong here: espionage fans would be very disappointed by this episode & others in this series, it's quite a change in direction the series takes here. It seems to me this show is also parodying corporate America: by this stage the two agencies are relating almost exactly like two corporations. You're either a 'Thrush man' or an 'UNCLE man'. This is actually a recurring gag in the series, the major difference being that you get a pension from UNCLE but Thrush kill you.
The awfulness of the musical disguises that the whole show thumbs its nose at so much American culture. Don't get me wrong, this is only an undercurrent at best, but this episode satirises both corporate America & the entertainment industry. Once again a sixties show - of course produced as part of the entertainment industry of corporate America - is postmodern enough to satirise its own medium. Of course much of the point is that the theatre & musical here are both a front, but The Man From UNCLE always manages to keep one foot in reality (to the extent of always thanking UNCLE for its co-operation in the credits), which is enough to suggest that the situation depicted here could be a real possibility.
Solo & Kuryakin remain firmly in role here. Kuryakin purely espionage man & Solo gets to chat up the girl. The thin plot is often criticised, but I don't personally find it a problem because there's a lot going on in characterisation & good touches to distract. The finale, where a fight between UNCLE & Thrush agents takes over the stage during the performance is good. For my favourite bit of this one I have reluctantly abandoned the scene where Illya is pretending to be a plumber for the scene where he puts on a turban & performs 'A Man is a Horn'.