The cartoon opens in Argentina with Mickey, as the notorious "El Gaucho", riding into town with his trusty emu (emus, not ostriches, are native to South America). That right there is comedic gold. It's interesting that Mickey plays this outlaw role, which of course is completely out of character today. Notice how now Mickey has gained shoes.
In the town cantina, Gaucho Mickey spots the charming dancer Minnie. Here she is portrayed as much sexier than in her previous film, what with her hips gyrating from side to side. As the character evolves over time, she will become less sensual and more mouse-next-door. Minnie also has gained shoes along with a bra.
This cartoon also marks the first appearance of Pete in a Mickey Mouse film. While Pete eventually becomes Mickey's arch-nemesis (and later the enemy of Donald, Goofy, and others), his true history extends beyond even that of Mickey and Minnie. Pete first appeared in the Alice Comedies of the 1920s, and once the production on those silent films ceased he found a home with the mice.
Pete's formula in these early shorts is almost always the same: he steps in to steal Minnie away for himself. That's exactly what he does here, and the storyline allows Mickey to be seen not as just a mischevious character but also as a true hero. As more and more cartoons are made, Mickey will ultimately pursue this hero personality and leave his naughty ways behind.
Like Plane Crazy before it, The Gallopin' Gaucho showcases a Mickey we today are not used to seeing; in fact, in this cartoon he is perhaps even more devilish than before. Mickey is seen smoking, which today is just plain crazy to see.
Mickey also downs a hearty mug of beer, which again is a true rarity today.
An interesting thing I noticed while watching this cartoon was Mickey's design. In the beginning, Mickey is drawn the same as he appeared in Plane Crazy (with shoes); once Pete is introduced, Mickey's facial design changes to his more familiar button eyes. Not only does this mark the first time this design is seen, but it's interesting that it occurs at the moment Mickey becomes a hero. It's amusing to think that Mickey changes not only his personality (which up to this point has been naughty) but also his appearance to reflect his more heroic and "everyman" design that becomes so popular later in his cartoon series.