The first Disney animated film without the strong involvement of Disney himself, this film suffers from the fact that the story is not particularly original or interesting (this is, I believe, the only animated Disney film since the 1940's which is NOT based on an earlier book or other work, but is rather an original story). As others have noted, the plot is essentially a cross between the romance in Lady and the Tramp and the kidnapping/journey home story in 101 Dalmatians.
But to overcome this flaw, the filmmakers have successfully used many of the better features of most of the Disney animated films of the previous 10-15 years: Phil Harris (from The Jungle Book) voicing one of the main characters, follows his duet with Louis Prima in the previous film with another here with Scatman Crothers. The quality visual look of this film is virtually carried over from "Dalmatians" (with some nice nods to French Impressionism, it appears), and the villain here (the butler) is strongly reminiscent of the henchmen in that film as well. (This is probably one of Disney's least memorable villains.) The main story goes back and forth between the cats, and the butler's ongoing difficulties with two rural hound dogs (with great voice work by Pat Buttram and George "Goober" Lindsey"). The various animal characters are similarly familiar to those who have seen "Tramp" and "Dalmatians." The cats' owner, while bearing a striking visual resemblance to the wicked stepmother in Sleeping Beauty, bears none of that character's nasty traits and comes across as very warm and generous.
The real strength of the film is the voice work; after first going toward the use of mostly familiar actors in The Jungle Book, the tactic is continued strongly here with Disney veterans Harris and Sterling Holloway from The Jungle Book, and Eva Gabor (who would do a very similar character in the later film The Rescuers), as well as Crothers and Nancy Kulp. All are excellent here, particularly Harris and Gabor in the leads. The character animation is as excellent as one would expect, showing a variety of emotions well.
Smaller children may be upset by a few brief episodes (an escape from the path of a speeding train, a near-drowning by one of the children), but these are not presented in a particularly frightening or dark manner and are over very quickly. Overall, there's very little of the type of more frightening scenes found in many other Disney classics.
One minor oddity is the way some visual aspects of 60's culture are depicted among the jazz-performing cats in supposedly 1910 Paris; one can't help but wonder why the story wasn't set solidly in the present, other than the great deal Paris had changed much of its appearance in the intervening time. It really would have made more sense that way.
The songs, while being pleasant and sometimes very enjoyably performed, are not particularly memorable. Nonetheless, the general energy applied here, the excellent voice work and fine animation all contribute to overcome the relatively few and minor weaknesses. Far from the greatness of classic "10"s such as Pinocchio or Aladdin, and not quite up to the "9"s one might give to Sleeping Beauty or 101 Dalmatians, this is probably a rather marginal 8 of 10; perhaps a 7.
