So Samus is a grounded zoning character with a really strong defensive game. She has good range, strong projectiles, and some of the best OOS options in the game. She doesn't have a great deal of safe, aggressive pokes, and her ability to safely challenge the air is limited, at best. Her gameplay is centered around her grounded pokes and solid whiff punish potential, as well as a very hard to counter edgeguard game.
ZSS, in contrast, is a movement based, bait-and-punish character with a good brickwall. She has good range and speed on her aerials, safe-ish air-to-airs, great combo potential, and a solid dash dance. Her defensive and OOS options, however, are sub-par, her projectile is underwhelming, and while her grabs are pretty decent, her throws are mediocre. She'll be utilizing the whole stage in order to bait out unsafe options from her opponent then get in and deal a lot of damage and try to set up for her pretty solid edgeguard game by knocking her opponent offstage.
It's less productive to compare the characters by asking what they have that is different, and a bit simpler to ask what they have in common. They both have pretty good edgeguard options that cover a lot and keep them pretty safe. Other than that, how they land their hits, how they capitalize on confirmations, how they set up for edgeguards, and how they play on defense are all balanced totally differently. Like Foo said, you won't find two more different characters, at least among those who are the same character.
Ok, I guess Zelda and Sheik are more different.
