In my opinion, this is one of the best classic science fiction movies ever made, right up with The War of the Worlds (1953), The Day the Earth Stood Still (1951) and Forbidden Planet (1956).
To us in 2011, its special effects might be laughable, and yes we know that you wouldn't fire a missile down a hole to punch into magma with a nuclear warhead. But it is a delightfully unique story of ingenuity that contains a major element that *has* come to pass, albeit not as the writers foresaw - the development of geothermal energy. It also showcases a time 55 years ago when no one had any idea what the inside of the Earth was like! The movie was based on best-guess geology, and what they developed made it fun. Further, it notes the potential dangers of messing with Mother Earth unless you're absolutely sure of what you're doing.
Many pieces of technology and social graces speak well to illustrate a period in history that many of us were either too young to remember, or not even born yet.
As I said, this is not Industrial Light and Magic, but the special effects are great for the period. I have and always will be a fan of using detailed miniatures.
I gave this movie a very high rating because it's just a good flick to sit down and watch. The story is fun and interesting, but not heavy. The science is wrong but at least they tried, and you have to smile at that. Astonishingly, the casting and acting is decent as well.
Be sure to find some time for this movie, and don't be afraid, this is *not* a 1956 version of "The Core." They are entirely different movies of both type and quality.