Like I said, When the Cat's Away is interesting because Mickey and Minnie are the actual size of the creatures they are supposed to be. The pair appear like this in only a few toons until their proper height is fully established.
Some truly clever gags are incorporated in this film. My favorite is the way Mickey and Minnie use the Swiss cheese as a piano roll to play music. It'll take a while to get through Mickey's other cartoons, but I'm pretty sure this gag is used more than once.
Another fun gag is the very inventive mouse record player. This gag for sure is used numerous times in various Disney cartoons; one of my favorite versions involves Pluto in the cartoon Pluto's Blue Note in which he manages to make all the girl dogs swoon over his "crooning".
As a side note, notice the mouse with the shorts in the picture above. During this portion of the toon, Mickey and Minnie are on the piano while these three mice find the records. Apparently some cartoonist made a mistake and drew one mouse with Mickey's costume. The problem is understandable since at the time the Disney animators were not as careful about such things; in fact the same thing can be seen in a later Mickey cartoon. In the coming years such mistakes would not be made in an effort to keep Mickey as identifiably unique as possible.