Story: Players who have not played the original version are introduced to Chaos, a mysterious being that absorbs Chaos Emeralds. Dr. Robotnik (Eggman) is trying to get his hands on the Chaos Emeralds in order to make Chaos more powerful. It's up to Sonic and his friends to stop Robotnik and Chaos. The adventure is seen through the eyes of Sonic the Hedgehog, Miles "Tails" Prower, Knuckles the Echidna, Amy Rose, Big the Cat, and E-102 Gamma. Each character has different types of stages to play.
Levels: The levels are the same as found in the original Sonic Adventure game.
Chaos Emeralds: No changes have been made with the Chaos Emeralds from the original Sonic Adventure game.
Miscellaneous: Players that played the original game will be happy to find out that the game has improved. For instance, the graphics are sharper and the colors have been darkened so that the game is easier to see. Loading times have also improved from the Dreamcast version. The music is the same as the original, however the Chao Race entrance music has changed. A Black Market has been added to the game where items for Chao can be purchased. And, just like Sonic Adventure 2 Battle, statistics on Chao are updated on-screen whenever a Chao begins to improve in various areas.
Another new addition is Mission Mode, which provides a new challenge to the original game. After beating a character's stages, the character is allowed to play Mission Mode. Missions are scattered around Adventure Stages, which provide a clue as to what the character must do in order to complete the objective. There are a total of 60 missions.
The following two additions have been classified as "secrets," meaning that they might be spoilers to people that have not played the game. First there is the addition of the original Game Gear games. All 12 Sonic the Hedgehog games have been placed in the Mini Game Collection. Game Gear games are obtained by earning emblems and completing missions. For emblems 1-100, a game is unlocked for every 20 emblems earned. Emblems 101-130 will unlock a game for every 10 emblems earned. For every 20 missions completed, a game will be unlocked. Finally, for getting all 130 emblems and completing all 60 missions, a game will be unlocked.
Game Gear Games Unlocked (listed
in alphabetical order):
Dr. Robotnik's Mean Bean Machine
Sonic Blast
Sonic Chaos
Sonic Drift
Sonic Drift 2
Sonic Labyrinth
Sonic Spinball
Sonic the Hedgehog
Sonic the Hedgehog 2
Sonic the Hedgehog Triple Trouble
Tails' Adventures
Tails' Sky Patrol
Aside from the Game Gear games, the other "secret" occurs when all 130 emblems are earned. Metal Sonic becomes available for play, but only in Trial Mode. The only stages that are available for play are all of Sonic's stages. The only visible changes that have been made (aside from seeing Metal Sonic) are the changes in the 1-up boxes to show Metal Sonic's picture. And, if you save the game after playing Metal Sonic, you will hear a different voice asking you what character/stage to select.