If you're thinking of buying this collection, chances are that you're most interested in F.W. Murnau's 1927 silent masterpiece Sunrise. (For whatever reasons Fox may have, this is currently the only official way to get hold of the Sunrise DVD.) My review is mainly aimed at those folks, so I'll try to answer the question: Is it worth buying the other three to get Sunrise?
Short answer: Definitely! Fox's DVD transfer of Sunrise, which is an upgrade from an earlier Laserdisc release, is superb. No kidding, it's actually comparable to the best current transfers of silent films, like Kino's Metropolis, WB's Chaplins, and Criterion's Passion of Joan of Arc. Considering that any of those titles would cost you about what you'll pay for this whole collection, you've got to figure that you're getting a pretty good deal.
Long answer: I actually believe that two of the other three films here are masterpieces in their own right. How Green Was My Valley, which has unjustly been labelled as the film that "stole" Best Picture from Citizen Kane, ranks among John Ford's best efforts; it's a genuinely beautiful, though an admittedly sentimental, film. And it's one of those movies that received a solid restoration a few years ago -- back when AMC actually showed good movies and took a hand in these sorts of projects. All About Eve, of course, needs no introduction. I find it a tad too long, but I agree that it has one of the best scripts ever written and some fantastic performances. It has finally received a full restoration from Fox -- all the speckles are gone (though some of the image's sharpness has gone, too). Gentleman's Agreement, on the other hand, is one of those movies that's easier to admire for its aims than for its entertainment value or aesthetics. It has dated badly, and Fox's lack of restoration work isn't likely to get it rediscovered any time soon.
So my opinion is that you get three great films (and one of historical interest) for a very reasonable price. Each title comes with quite a few extras, if that matters to you -- though here again I think Sunrise benefits from the most informative and interesting extras, including a semi-reconstruction of one of Murnau's "lost" films. Highly recommened!