Sonic Forces is good. Sure, it's short, but the game is very fun.
Except during the autoscrolling.
Forces is a flawed game with tons of potential. It needed better controls, longer levels and better paced plot.
Modern Sonic controls like he is on rails, most of the time it feels like you are forced to go somewhere and trying to move somewhere requires a herculean amount of effort, like in the Aqua Ruins U-shaped road, there is an alternative path but getting there is painful because the camera and the controls try to fight you.
Classic Sonic plays like he is underwater during all the game, getting speed is hard and its momentum is too floaty. Spin Dash doesn't help and Drop Dash seems to just fling you into a straight line really fast and then slows down like hell, making it unreliable and even suicidal in some scenarios.
Avatar somehow plays the best, and in general is a pretty fun character to play, but he doesn't get too much speed (because he is not Sonic) and the Wisp-On abilities are really fun but very OP. I think it would have been better to get Wisp-On powers on the stage instead of picking one and going with it, plus not being able to change species until the end of the game was kinda weird.
The level design is arguably the weakest part. It is like they tried but ran out of time. There is a lot of attempts at branching paths but they always converge into a main one, and interesting concepts like Operation Big Wave/Metropolis where the stage would just fall apart and get crazy, but it was underused as hell. The QTEs obviously felt off in a Sonic game and the bosses were rehashed in the game (The Metal Sonic/Infinity combo and the final boss being a combo of Egg Dragoon + straight out of Sonic Colors), which makes the game feel even shorter and cheap.
And last, but not least, the plot. They tried to hype it up as something serious and all, with all the "All major villains are back, Sonic gets captured for months, Eggman takes the world" but then Sonic gets out and it goes exactly like the usual, and the Phantom Ruby mystery gets solved in a sudden asspull with Shadow and you don't even get to fight other nostalgia bosses. Zavok's inclusion is mostly author appeal (like the Wisps) and feels off compared to the other classic bosses. Also Classic Sonic is irrelevant to the plot and the game would have been better without him, the retcons to previous games just makes it all worse.
The OST is pretty good except for some Classic songs, but they also grow on you over time, so there is also that.
As a disclaimer, I somehow triple dipped Sonic Forces (Got it for cheap on PC, bought on Switch for portability and got it as a gift on PS4) alongside Mania and played it more than a normal person would. It is not a great Sonic game, but it is a decent time killer with unique ideas and flawed execution. IMO it would have been a lot better if they focused on making a solid 3D game and without trying to cash in Classic nostalgia. IMO Takashi Iizuka should step down from Sonic Team for now and let new blood into it, or maybe work alongside the original major players from Sonic Team and Mania Team into an attempt to get the best from past and future.