Interesting both in itself and as a reflection of its era, "The Day the Earth Stood Still" may seem unspectacular now to those who are used to the extravagant science fiction pictures of the present time, but it deserves its place as a cinema classic. The story is worthwhile in itself, and as soon as you set aside any preconceptions about what science fiction should involve, it also builds up some pretty good drama and suspense. Its perspective is also interesting to see as a reflection of the concerns of its era, which have such obvious similarities with those of the present.
The story itself sometimes moves rather slowly, and the focus is really more on the reactions to Klaatu's arrival than on the action itself. As Klaatu, Michael Rennie stays pretty low-key, as does the rest of the cast much of the time. Although there are times when the movie might lack some energy as a result, in general it probably works better that way than it would have if there were too much forced emphasis on the urgency of Klaatu's mission, which is more than able to speak for itself. The ideas behind the story are fairly simple, but they are, of course, just as significant now (or in practically any other era) as they were in the 1950's.