These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Big Lipped Alligator Moment: The rather excessively long slapstick chase sequence that happens when Edgar is trying to dump the cats in the countryside. After he loses the basket, the chase still goes on for about five minutes and the whole plot about the cats being abandoned has to stop while we wait for the chase to end.
Even the main characters comment on it. "I like Uncle Waldo." "Yes, especially when he's 'marinated.'"
Unfortunately, this was also Bill Thompson's final role in an animated film, due to him dying of a heart attack a few months later.
Stop Helping Me!: O'Malley's reaction to Abigail and Amelia, who are under the mistaken impression that he's trying to teach himself to swim when he's really just trying to get to shore after saving Marie.
Values Dissonance: If the film were made more recently, it's seriously doubtful they'd be able to get away with having an Asian cat who has crooked eyes, buck teeth, a thick accent, and who plays the piano with his chopsticks, playing a 'Chopsticks' style melody filled with Asian buzzwords.
The entire plot hinges on the fact that Edgar apparently believes cats literally have nine lives. There is also that fact that the Disney Encyclopedia writer, John Grant, points out that had Edgar obeyed the wishes of the will, he would have had a guaranteed job taking care of Madame's "heirs" until he almost certainly outlives them and gets the remainder of the inheritance all for himself.
Not to mention he miscalculates how long they'll live; cats live about 12 years, on average. (This is accurate to some degree as, some live to 18). He believes they have nine lives, and there are four cats altogether. He then does the math; twelve, multiplied by nine, multiplied by four. He's forgetting that the cats aren't going to take turns aging.note At the very least, he admits he got that wrong immediately after.
It is a Disney movie after all, so for all we know, Disney cats actually do have nine lives.
Not to mention, well, they're freaking cats. As Edgar was the only human beneficiary, and cats have little need or use for money, the will basically was saying Edgar gets everything, as long as he takes care of the cats.
At the very worst, Edgar would need to take care of the cats, then later on the offspring of the cats. And he could probably justify hiring somebody who really likes cats to take care of them as well. Considering that for this small task he will become a millionaire, it's not a lot to ask. Edgar really isn't very bright...