"Lifeboat" is an excellent film. It is a great achievement by Alfred Hitchcock that he could create a film set on only a lifeboat interesting for its duration. Hitchcock had a knack for experimental films, such as "Rope", which seems to be one continuous shot, and "Rear Window", which features one small apartment and a man in a wheel chair. With so little, he is always able to do so much.
In "Lifeboat", we start out with the sinking of a ship and people gathering on the lifeboat. It's really that simple. This is a character driven film. There are no lush chase sequences, there are no gunfights, there is no mystery. Nope, its all about how this collection of characters interact with each other. Its a study of how difference of opinion can creat tensions, and how people can deal with those tensions. Its really fascinating to watch, and when its all said and done, you get the impression that it wasn't just an experiment, but that it had something to say, and it did.
The only slight flaw in the film is that we don't really get a sense of how long(exactly)they've been at sea. I "Cast Away" we saw Tom Hanks lost a considerable amount of weight and grow a considerable amount of hair. Well, that is the one thing you don't see with this movie. Its really a minor quibble anyway because it doesn't diminish the entertainment value at all.
Hitchcock was the master of suspense, but he was never afraid to try other things, from screwball comedy(Mr. and Mrs.Smith) to psychological thrillers(Vertigo). This film is definitely one of his best and most interesting experiments. 9 out of 10.