The goal is to complete different levels under the roles of film protagonists Nemo, Marlin or Dory. It includes cutscenes from the movie and each clip is based on a level, e.g. hopping through a batch of jellyfish. It was also the last Disney/Pixar game developed by Traveller's Tales.
- Marlin: Marlin is one of the three playable characters in the game. Marlin is a clownfish who bravely journeys through the sea to search for his lost son Nemo, with the help of a forgetful, but friendly fish named Dory.
- Nemo: Nemo is one of the three playable characters in the game. Nemo is taken from his father Marlin by a diver who puts Nemo in a fish tank in his dentist office. Gill and the other tank gang members help Nemo escape the fish tank and find his father.
- Dory: Dory is one of the three playable characters in the game. Dory is a blue tang and she assists Marlin in his journey to find his son Nemo. Dory suffers from short term memory loss, causing her to forget things instantly after she says something.
- Gill: Gill is a moorish idol who is the leader of the tank gang. Gill is determined to get Nemo, the other tank gang members, and himself out of the dentist office and into the ocean. Gill appears in the "Mount Wannahockaloogie", "Training with Gill", and "The Plan" levels.
- Bruce: Bruce is a Great White Shark who appears in the "Minefield" and "Submarine" levels. Bruce invites Marlin and Dory into his submarine for a meeting, but goes into a feeding frenzy when he smells Dory's blood. Bruce, who has just completely lost it, chases after Marlin and Dory, who tries to avoid being eaten by him. Bruce is the only character in the game to have a different voice actor in the movie, being voiced by Jess Harnell rather than Barry Humphries.
- Tank Gang: The tank gang is a group of friendly fish who Nemo meets in the dentist's fish tank. They help Nemo get out of the dentist's office and find his father Marlin. Each member of the tank gang appears in the "Hide & Seek", "Mount Wannahockaloogie" and "The Plan" level (with the exception of Peach who doesn't appear in "The Plan" or "Mt. Wannahockaloogie"). Bloat is the only member to come in the "Training with Gill" level. All tank gang members are voiced by their original voice actors.
- Bloat is the pufferfish who swells up when he's angry or surprised.
- Gurgle is the neurotic, nervous royal gramma who hates germs and being dirty.
- Jacques is the French cleaner shrimp who loves cleaning the tank and doesn't want a single mess in it.
- Bubbles is the "bubble-obsessed" yellow tang who loves chasing after bubbles.
- Deb is the black and white humbug who believes her own reflection is her sister, whom she calls "Flo".
- Peach is a starfish who spends her time sticking to the wall of the fish tank studying what the dentist does and alarming the other tank gang members when something important happens.
- Tad, Sheldon and Pearl: Tad the butterfly fish, Sheldon the seahorse, and Pearl the flapjack octopus are the three students who Nemo befriends on his first day of school. They appear in the first three levels in the game: "Going to School", "Field Trip" and "The Drop Off".
- Whale: The Whale is one of the allies in the game. He assists Marlin and Dory go closer to the dentist office where Nemo is. The Whale only appears in the "Whale Chase" level where it swallows Marlin & Dory, who think its trying to eat them. You play as Dory to escape from the Whale's mouth.
- Anglerfish: One of the major enemies in the game. Marlin and Dory meets the anglerfish when they go to the dark abyss in search for the diver's mask. The anglerfish first appears in the "Mask Search" level where it tries to eat Dory if she goes too far from the current mission area, and in the "Anglerfish Chase" level as the main enemy where you have to avoid being eaten by it.
- Jellyfish: Jellyfish are common enemies in the game. Little jellyfish appears in early levels of the game, while the larger ones appear in the "Jellyfish Race" level, where you play as Marlin to beat Dory in a race to get through the jellyfish forest first.
- Mr. Ray: Mr. Ray is a spotted eagle ray who is Nemo's science teacher. He appears in the "Field Trip" level where you have to keep up with him and not get separated.
- Crush: Crush is a sea turtle who is one of the allies Marlin meets in his quest to find Nemo. Crush only appears in the "East Australian Current" level at the end where he tells Marlin and Dory to go through the current to advance to the next level.
- Moonfish: The moonfish are one of the helper characters in the game. In a race or a timed challenge, the moonfish form an arrow towards where you have to go. They also appear often in bonus levels throughout the game.
- Krill: The krill are used for protection throughout the game. When you find a krill, it follows you and you don't lose lives by enemies until there are no more krills following you.
- Going to School
- Field Trip
- The Drop Off
- Mask Chase
- Catch Dory
- Hide and Seek
- Mask Search
- Anglerfish Chase
- Mount Wannahockaloogie
- Jellyfish Race
- Training With Gill
- East Australian Current
- The Plan
- Whale Chase
- Treatment Plant
- Fishing Net Rescue
- Albert Brooks and Jess Harnell - Marlin
- Ellen DeGeneres and Jennifer Hale - Dory
- Alexander Gould - Nemo
- Willem Dafoe - Gill
- Barry Humphries and Jess Harnell - Bruce
- Brad Garrett - Bloat
- Joe Ranft - Jacques
- Austin Pendleton - Gurgle
- Vicki Lewis - Deb
- Stephen Root - Bubbles
- Allison Janney - Peach
- Erica Beck - Pearl
- Jordy Ranft -Tad
- Erik Per Sullivan - Sheldon
- Bob Peterson - Mr. Ray
- Andrew Stanton - Crush
The game received mixed reviews for its colorful regions, mini games and adventures. However, the game received much lower scores for its other unfinished graphics and its enormously frustrating gameplay; the difficulty increases largely in levels such as "Catch Dory", "Minefield" and "Jellyfish Race", among others, for their quick nature and puzzling structure.