Sonic Heroes features team playing action. There are three characters per team, and each team has its own storyline. Each character fits into a category: speed, flight, and power. The teams are:

~ Team Sonic (Sonic the Hedgehog, Miles "Tails" Prower, and Knuckles the Echidna)
~ Team Dark (Shadow the Hedgehog, Rouge the Bat, and E-123 Omega)
~ Team Rose (Amy Rose, Cream the Rabbit, and Big the Cat)
~ Team Chaotix (Espio the Chameleon, Charmy Bee, and Vector the Crocodile)

Team Rose is for beginners, Team Sonic has a medium difficulty level, Team Dark is difficult, and Team Chaotix has mission-based team play. Mission-based play means that there is a goal to accomplish. For instance, "find 10 hermit crabs" is the first mission. The game recommends playing Team Rose if you're new to action games. (Regardless of whether you've played an action game before, I highly recommend playing Team Rose first. The stages are shorter and your Team Blast gauge charges faster.)

Story: The background story is different depending on the team. Team Sonic's story begins when Tails and Knuckles give Sonic a letter from Eggman detailing his latest scheme for world domination. For Team Dark, their story begins when Rouge explores Eggman's base for treasure and finds Shadow in a stasis capsule. She awakens Shadow, and in the process accidentally activates Omega. The three team up to go after Eggman. Team Rose's story begins when Amy runs into Big and Cream. Amy is looking for Sonic, Big is looking for Froggy, and Cream is looking for Cheese's twin Chocola, so they team up to search together. Team Chaotix begins their story when they receive a request to take on a case. Although Espio is suspicious of the message, Charmy and Vector are ready to take the case without hesitation.

Levels: There are 14 levels for each team:

Seaside Hill
Ocean Palace
Grand Metropolis
Power Plant
Casino Park
Bingo Highway
Rail Canyon
Bullet Station
Frog Forest
Lost Jungle
Hang Castle
Mystic Mansion
Egg Fleet
Final Fortress

If you have beaten the game with all four teams and collected all seven Chaos Emeralds, then the last boss will be unlocked: Metal Madness and Metal Overlord. There is also a tutorial stage called "Sea Gate," which allows you to practice with your team. Since it is just for tutorial purposes, it does not save the progress made in the stage.

Chaos Emeralds: There are seven Chaos Emeralds to collect in the game, and any team can collect the emeralds. Chaos Emeralds are found in special stages. In order to enter a special stage, you must find a Special Key in an even-numbered stage and complete the stage. (Finding the key in an odd-numbered stage will take you to a special stage where you can play for extra lives instead of an emerald.) The emerald races toward the end of the stage, and the team must catch up to the emerald before it reaches the end of the stage. Obtaining all seven emeralds unlocks the final boss battle: Metal Madness/Metal Overlord.

Miscellaneous: An interesting addition to the game is the Team Blast. This gauge is charged by performing various actions such as collecting rings or using the flying formation's Thunder Shoot. Once the gauge is full, the Team Blast attack can be executed. This attack involves all three characters and destroys all enemies within a specified radius. You will score more points for using Team Blast based on how many enemies are destroyed. In addition, Team Rose will gain invincibility after executing this move, while Team Dark can move while time stands still (i.e. Chaos Control).

There are two missions for each game. The first mission is relatively simple; most first missions are just to complete the stage, with the exception of Team Chaotix. The second mission can only be accessed by selecting "Challenge" from the 1-Player menu. The second mission varies per team:

~ Team Sonic: complete a stage within a time limit (for an A-Rank you must obtain a certain amount of points)
~ Team Dark: defeat 100 enemies (for an A-Rank you must meet a time limit)
~ Team Rose: collect 50 rings (for an A-Rank you must meet a time limit)
~ Team Chaotix: collect all items or finish a stage within a time limit (for an A-Rank you must obtain a certain amount of points)

Interesting observations/facts:
~ Omega (a robot) is a new character to the Sonic universe
~ For Charmy and Vector, this is their first appearance since they debuted in Knuckles· Chaotix (Espio last appeared in Sonic the Fighters)
~ You have to collect all seven Chaos Emeralds in this game--which you didn't have to do in the Sonic Adventure games
~ There are 120 emblems to collect
~ The GameCube version was released at the beginning of January, while Xbox and PS2 users had to wait until the end of January
~ Every 20 emblems earned unlocks a new 2-player game
~ When all A-Rank is achieved, Super Hard Mode is unlocked

Super Hard Mode is playable with Team Sonic. Play begins with the first stage and proceeds forward, skipping the boss stages. Just as the name suggests, the stages are harder than the original version of the stage. In addition, once you lose all of your lives the game is over and you must start Super Hard Mode from the beginning.