I'm not a fan of shows doing an entire episode in homage to another show, but given than Star Trek is not only a culutral land-mark, but undoubtedly the biggest influence on Futurama after The Simpsons, so it's completely justified.
The fact that they got the entire surviving cast of the original series of Star Trek in as guests just amplifies the episode's already high quality. Not only are they all nerderiffic celebrities, but they all have distinctive voices and they're all actors so their performances are great.
The plot is wonderful as it's basically a perfect amalgamation of every Star Trek plot ever, but doesn't feel contrived or gimmicky. The gags are also brilliant. It definitely helps to know your Star Trek, but frankly if you don't have a basic knowledge of the show, you've been missing gags on Futurama for years. Every possible joke that hadn't already been made about Star Trek is made here. The jokes are all hilarious and the fact that so many are delivered by the cast of Star Trek whilst being about the cast of Star Trek makes it all better.
Add on to that some wonderful animation and some of the best music in Futurama's entire run and this episode is a true gem -to the point that Family Guy attempted to capture the same lightning in a bottle a few years later with The Next Generation... but as usual Futurama was far better.