Minish Cap is no doubt the best Zelda game on GBA.
The story of Minish Cap is somewhat simple. An evil lord named Vatti unleashes an ancient evil on to the land of Hyrule after opening a chest full of demon faces that was sealed by the Legendary Picori Sword by using his evil magic to break the sword's seal (oh no!). Then on top of that he turns the princess into stone! It's up to the hero, Link (or whatever you call him, personally I named him Russ) to collect the elements and defeat Vatti... at least that's how I interpreted it. Early on your quest you meet a talking bird hat named Ezlo, which gives you the power to shrink yourself to the size of a pea, which also opens up a brand new world to the hero, the world of the ancient Picori people known in the legends. Link then has to collect the four elements and PWN Vatti outta Hyrule and rescue the Princess!
The gameplay of Minish Cap is very simple. The screen shows you your hearts (life) and a few images of buttons on the left: "A" (lets you equipt and use an item with the "A" button), "B" (lets you equipt and use an item with the "B" button), and "R" (let's you roll when walking, open up doors, talk to people... basically the action command). The game has an over head view, and moves on a grid (although some spots scroll). Overall the gameplay is very fun and easy to get into. Hackin' and a slashin' with the sword is also very entertaining, but you get a wide variety of other weapons too (like a boomerang, a bow, and even a magical jar of wind... yeah).
The music of Minish Cap is good as well, but I'm not a guy who obsesses over video game music, heck, I played most of Minish Cap with the sound off...
Overall, Minish Cap is a great game. I really enjoyed it, and I actually played through it twice. I rarely ever replay my games. I recommend everyone to try this game out sometime.