There are times when I get a little persnickety about the most minor of things.
For example, Leslie Nielsen's recent passing - although he's getting much attention for his comedic work (Airplane, Police Squad, the Naked Gun Trilogy) - and deservedly so - his previous dramatic work may get short shrift. He was one of the most active character actors pre-1980s...and one of his films deserves much wider attention (as in, "Hey, pal Chuck, here's an obvious blog post you can link to on Comic Related").
Admittedly, there is a very soft spot in my heart for Forbidden Planet - it was one of the few movies that my father and I could both enjoy (it was the first movie he had ever seen), but in looking at it objectively, it's a really solid movie, and is a very atypical 1950's science fiction film.
As others have stated, it does seem like a dry run for Star Trek, but taken on its own, Nielsen serves to provide a solid grounding for the sheer otherworldliness of Forbidden Planet. If you're looking at the roots of Nielsen's comedic chops, look at his performance as Commander John Adams in this book - in short, the reason his comedic performances work is that he essentially can serve as his own straight man. (You also might want to check out the Columbo Season Five episode "Identity Crisis" in which Nielsen goes toe to toe with Patrick McGoohan).
But what also works is that the film connotes a total otherworldly atmosphere - from the electronic background sounds to the production design, from the concepts in the script (a clever mixture of Shakespeare's Tempest and Freudian thought). In short, much contemporary science fiction - Star Trek, Twilight Zone, Doctor Who, and others - can be seen as having some tentative roots in this film.
(Plus, if you're the Chris Sims-style aficionado, there's a robot that is able to make booze. Trust me on this)
We're moving towards an age where actors who worked during the "Golden Age" of Hollywood will soon be no longer with us...and Nielsen did provide many comedic moments.
But his true strength, in my opinion, lies in some of his previous, dramatic work.
See Forbidden Planet. Now.