- We're keeping the original six characters -- Sonic, Tails, Knuckles, Amy, Big, E-102 Gamma.
- All of the original eleven stages will be present, plus two more.
- The Adventure Fields are the same: Station Square, Mystic Ruins, and the Egg Carrier.
- The items are all the same, with the addition of the Eggman and previously scrapped Time Stop monitors.
- The plot is more or less the game, but has several changes to try and make it more logical, and isn't as necessarily complicated.

- At least three characters will have entire gameplay changes. This obviously includes Big the Cat.
- There are plenty of physics changes to try and let the reboot run more smoothly than the original game.
- Many of the stages receive layout changes to prevent accidental glitching out and unnecessary death.
- Every action stage is separated into three Acts, to shorten the lengths of the levels.
- The Adventure Fields have very different layouts to try and make the action stages more accessible. In fact, Mystic Ruins has a much more drastic change to its jungle area, having a less confusing layout and a few huts.
- The item monitors take their design from the ones introduced in Sonic the Hedgehog 3.
- The Chao Garden prevents characters from using attack commands to prevent accidental abuse of Chao, and the only way now to do such is by throwing Chao. But would you really throw a Chao?
- Knuckles' stages feature "black rap".

Gameplay Changes~
- Sonic now explores all stages, Tails, Knuckles, and E-102 Gamma explore ten of them, and Amy and Big access five of them.
- Sonic is slowed just enough so that he doesn't run into walls as much, although he remains quite fast. In addition, his homing attack has easier execution, and red crosshairs appear over enemies that can be reached by it. Sonic's spindash can be charged up, and has more free movement than it did in the original version. The light speed dash now works like it did in Sonic Adventure 2: when Sonic is next to a ring, all he needs to do is press the B button. The Ancient Light is now an optional upgrade, but there is a new mandatory option for Sonic to do a "Drop Dash". The action stages featuring Sonic are somewhat changed in order to fit his revised mechanics, too. In addition, Tails no longer follows Sonic in Action Stages unless the player is playing Trial mode. Otherwise, the way Sonic plays his stages is identical.
- Tails' gameplay no longer has him beating Sonic to the goal ring (or in the last stage's case, Dr. Robotnik). Instead, he moves through some of the same stages as Sonic, although he has to occasionally take alternative routes as the places Sonic went through are often blocked off. Tails now gains the Rhythm Badge in his first level, Windy Valley, and has to utilize his tail swipe to defeat most enemies and has to fly around to reach higher places. Otherwise, Tails' gameplay in his stages is fairly identical.
- Knuckles' gameplay is similar to what it was in the original Sonic Adventure, with the focus being to find the Master Emerald pieces. The stages are doubled in size, and Knuckles' emerald-finding senses have sharpened to the point where if Knuckles is a quarter of a stage away from a Chaos Emerald, the radar will flash blue. Knuckles, once he gains the ability to do such, no longer has to go through an awkward effort to dig: it works like how it did in Sonic Adventure 2, with Knuckles able to skydive and dig, or press B on a wall to dig through it.
- Amy's gameplay has completely changed beyond the fact that she is being chased by ZERO. She is now a much faster character, and has the Warrior Feather by default. Her stages are no longer about being slow and solving puzzles, they instead change so that Amy has more combat-oriented gameplay, able to fight multiple enemies at once. Amy gains a slew of new abilities via collecting power-ups, and most are updates to her hammer. Her stages are doubled in length, too. In the Adventure Fields, Amy can now fight other bosses beyond ZERO, although the chaser still is her final boss fight.
- Big's gameplay, like Amy's, has drastically changed. Instead of pointlessly fishing, Big uses his fishing rod for solely beating on enemies (like how he could in Sonic Heroes) and can gain upgrades to his lure that allows him to attach weapons to it and take on multiple enemies within a long radius. Big is still a slow character, but has no problem dealing with ranged foes. He can cast his fishing rod to take items from a distance or break item monitors from afar, as well. His stages aren't too long, but require knowledge on solving simple puzzles in order to open up new areas.
- E-102 Gamma has the least changes to gameplay. Apart from having a slew of new stages to traverse, Gamma has more firing options and has more time in his stages, and has his stages doubled up in size. All his bosses -- the E-Series -- now have much more unique weapons, and Gamma can take them himself upon their defeat. This means that Gamma can now switch between weapon types in order to take on different enemies. Otherwise, Gamma's gameplay is identical to how it was in the original Sonic Adventure.
- Metal Sonic was originally just a palette swap of Sonic, but he can now use the Black Shield as a defense mechanism and the V. Maximum Overdrive Attack to cross long gaps and to explore areas that Sonic couldn't reach otherwise. He is also lighter and floatier than Sonic, and has his very own voice clips. In addition, people react differently when they see Metal Sonic, and in boss fights where Dr. Robotnik is involved, he remarks on his own creation turning against him, and refers to him by his real name.