A good episode in a mediocre season. This is partly due to the fact that it uses one of the better elements of the show, the fraternal relationship of Niles and Frasier. Add to that the very recognisable theme: things you liked in your youth may seem quite silly later on in life. Regular users of tv.com can attest to that: some show you loved as a kid comes out on DVD ... and you wonder what the fuzz was all about.
Irony is never far away in "Frasier", from Frasier's disdain for sci-fi (although Kelsey Grammer played in Star Trek) to the appearance of Derek Jacobi (Frasier professed to be a fan of "I,Claudius" in one of the "Cheers" episodes.) I was also delighted to see Patrick Macnee in his cameo role, though I presume Peri Gilpin was probably even more excited.
Another reason for this episode's success may sound strange: Daphne's not in it. With Jane Leeves being granted maternity leave, Daphne could disappear for a while, making it possible to ignore the Niles-Daphne plot line, the very thing that slows down episodes in this season.