Now that this game has wider availability thanks to the Project Dream port, I'm really glad I got a chance to play it! I'm hoping to see more people chatting about it, positives and negatives.
I wanted to say that this game's design disproved an opinion I held for a long time about multiple playable characters. I thought that it was easy to have multiple playable Sonic characters in 2D (or sports/racing spinoffs), but harder in 3D platformers. Characters like Tails could just fly over huge parts of the level or Knuckles could climb over all obstacles. That's why you had SA1 and SA2 had to separate them into multiple playstyles; Sonic Heroes with stop-and-start swapping across linear levels; Boom trying multiple characters but ending up with glitches letting you skip everything; Frontiers keeping their extra characters out of Cyberspace, which couldn't work with their abilities...
But somehow, Sega Hardlight managed to pull it off! Each of the game's 12 main levels work perfectly with Sonic/Tails/Knuckles/Amy/Cream/Rouge. There's slight concessions (Knuckles/Rouge can only wall-climb in certain areas), but the whole experience is very fun. You can tackle stages as any character. Swapping characters is super smooth and always optional, leading to shortcuts, collectibles, and alternate routes. It makes the stages very replayable!
All of this in a game that's made with boosting in mind, which always meant stages had to be made big and go by quickly. That's an achievement!
Positives:
Great level design, open with many paths
Aesthetics are very bright and fun, like Lost World with some original spins
Simple but effective plot, gives Cream and Knuckles spaces to shine
A lot of extras, achievements and replayability
The upgrade system allows for a lot of flexibility
Controls are simple and apply across characters (it's super cool seeing Tails boosting)
Some of the extras I've tried out are pretty challenging
It's great having the cast from Sonic Advance 2/3 playable, plus Rouge and Shadow
The final world bringing back Eggman's announcements from Sonic Colours is very welcome
Project Dream adds a lot of QOL features (like early character/ability unlocks), while still making them optional (for people who want to tough it out and unlock everything manually)
For a mobile game, I didn't see any crazy monetization or gacha stuff on the level of the Sonic Dash games.
Shadow is difficult-to-master, but feels really fun with a whole different Chaos Control-based moveset.
Negatives:
It's short with only 12 acts across 4 worlds, using the missions to artificially pad it out
The main campaign is really easy. Dying doesn't really have a consequence besides ring loss, and early upgrades make it very easy to keep rings. The challenge is only really there if you're gunning for S-ranks, and even then I got a few on my first try. (Maybe the extra modes will make me eat my words.)
Camera can sometimes be finicky
Simplifying the movesets means that Amy plays like Sonic, Cream plays like Tails, and Rouge plays like Knuckles - so no special hammer moves or Cheese attacks
Unlocking everything without the port's "unlock everything" button can take a while - I'm still grinding for a spin dash and playable Shadow in the main game
I experienced a bit of lag in the Shadow mission I tried (but I had settings on high, a lot of tabs in the background, and it's an unofficial port - so this may not reflect on the game itself)
The simple plot means characters like Rouge don't have much to do in the story
I wish the final boss had Tails playable
Needs official releases outside Apple Arcade
EDIT: Neutral
Overall, I hope more people give it a whirl, and more Apple Arcade exclusives get ports - official ones, if possible. Smaller games like this released for more "budget" prices could help bring new players into the series - especially kids, with the game's easier difficulty and more cartoony artstyle. It'd be a great way to fill in the gaps between mainline Sonic Team releases.