This movie is pretty enjoyable in my opinion. I love the storyline, the cast, and, of course, the cat himself.
That said, the only issue I have is the MPAA rating. Supposedly, this film is rated G. Perhaps, in 1978, the content shown was suitable for all audiences. Today, this could easily pass for a PG rating, if not PG-13.
Violence ---
(1) Jake (without his collar) attacks a military man driving a jeep and we see the cat biting and clawing his face up-close! Fortunately, we don't see the results of this attack (otherwise, it would have been rated R and Walt Disney could never have made the film).
(2) The secret agent falls into a dumpster and is literally "thrown out with the trash" as he winds up inside the garbage truck.
Intense scenes ---
(1) The opening where the farmer sees the spacecraft for the first time and is upset with finding this discovery.
(2) General Stilton and his men attempt to arrest Frank and his friends before Jake freezes them. In a similar scene, Jake freezes a man with a dog at the army base before the violent scenes listed above occur.
(3) The main villain and his henchmen hold Frank's friends for ransom and won't release them unless they get Jake's collar.
(4) The big climactic chase scene is very intense. Two moments, in particular, are especially intense. In the first, Frank briefly holds on for dear life when Jake flips the plane upside down for several seconds. In the second, the villains open fire at Frank's plane in attempts to kill him...although they fortunately miss.
Objectionable content ---
(1) General Stilton's shirt reveals an attractive woman in revealing attire after his uniform is taken by Frank.
In my opinion, this is a film that deserves a PG-13 rating. Disagree all you want. I'm not changing my opinion just because people want to believe it's a family-friendly film with nothing bad in it.