I saw this film for the first time when I was seven years old. It scared the crap out of me but I couldn't stop watching it. It was then that I knew I was hooked on horror. "Creature from the Black Lagoon" is the perfect creature film. The cinematography on the underwater scenes is breathtaking and was innovative for its time. Ricou Browning, who is uncredited in the move, played the Gill Man in all these scenes. His work is remarkable. He brings a physicality to the Creature that makes you forget that you're watching a man in a costume.
The story has a "man vs. nature" plot line and is set in the Amazon [although the scenes were shot in Florida]. In this case the humans are on a scientific expedition where they discover the mysterious Gill Man whom, of course, they try to capture. The Gill Man returns the favor by kidnapping the fiance of one of the scientists. It's basically King Kong retold underwater! The acting is impeccable and the scene where Kay Lawrence does an underwater ballet in her torpedo bathing suit while the creature watches from afar is priceless. The beauty of the film is that it leaves the viewer rooting for the creature instead of the stupid, misguided humans. I love it!
There are several editions of this film out on DVD. My personal favorite is the two CD set from the Universal Legacy Collection which includes not only the original film but also it's two sequels: "Revenge of the Creature" (1955) and "The Creature Walks Among Us" (1956). All three are beautifully restored, although I would argue that the third film is far less effective than the first two. This DVD set also includes an excellent documentary "Back to the Black Lagoon" which examines the making of all three films as well as their influence on other filmmakers.
I don't believe you can watch this film legally anywhere online. If you know differently, let me know. This film is required viewing for any serious fan of horror.
For more info check out the film's entry in IMDB.