Hugh Harman, of Harman-Ising fame, directed this cartoon while he and Rudolf Ising were at MGM. For the most part, their cartoons kept to the old big-eyed, anthropomorphic animal style that had served them well. Many of these cartoons now look much too syrupy sweet, and looking back, simply aren't as funny or entertaining as the kinetic cartoons of Tex Avery or the anarchistic output of the boys at Termite Terrace. A good summary, in my opinion, goes along the lines of this: adorable, diminutive, singing, humanoid mice/birds/squirrels/kittens triumphing against an ugly, huge, sneering, humanoid owl/cat/dog/wolf/rat attempting to devour them, with little of interest along the way. Well, maybe of interest to Furries, but as for me, pass.
But this one is different. There's no real villain in this cartoon. This one actually explains why there are all these animals with a human-like society. This is the one that answers the nagging question, why aren't there any real humans to be seen? And unlike so many other, now unwatchable, cute talking-animal-with-clothes cartoons, this one actually has little cuteness, contains realistically-animated human figures, and ultimately tells a dark tale, indeed. With its bait-and-switch story construction, where it first looks like typical funny animal fare and goes on to tell, dramatically, the story of the last two men on Earth, I can't help but speculate what kind of impact it must have had on its World War II audiences. It may well be the first theatrical animation with a serious theme, and let me tell you, it works. It is considered by some to be Hugh Harman's best cartoon.
Cartoon Network shows it a few times each year as part of its Christmas programming, in the Toonheads Christmas Special. You may still have time to see it this year, if they show it again on Christmas Day. Worthwhile, not only for this cartoon, but also for the only Tom & Jerry Christmas cartoon, The Night Before Christmas.
Sources:
Toonheads (on Cartoon Network)
http://www.toonzone.net/early-years/creators/harman-ising/
http://www.toonopedia.com/mgm.htm