Sonic Forces is the latest Sonic the Hedgehog game to come from Sonic Team/Sega, since the release it's received mostly good or okay scores, then there are the others that don't particularly like it. So, whats my opinion?
The story of Sonic Forces might actually be the darkest story and game in the entire franchise. Eggman is plotting to take over the world and has gathered an entire army of robots, as well as a new friend known as "Infinite", who completely trashes Sonic and imprisons him on the Death Egg for 6 months, allowing Eggman to conquer 99% of the world. During this time, Infinite encounters the Avatar, who will later become an ally and free Sonic, they also discover that Metal Sonic, Zavok, Chaos, and Shadow are all replicas created by the Phantom Ruby, who had traveled into the future along with Classic Sonic, who easily defeats a Chaos replica and saves Tails. Sonic and the Avatar get through various obstacles and fight Infinite multiple times, who they eventually defeat and send him back to Eggman's base. Eggman then uses the real Phantom Ruby to upgrade the Death Egg Robot, but is defeated by the two Sonics and the Avatar, saving the day and prepare to clean up after the war.
Sonic and Classic Sonic keep their usual snarky and silent personalities, Tails however, is not in his best shape, as when being encountered by Chaos he screams for Sonic's help, although he's fully aware that Sonic is imprisoned in space. Knuckles is now leading the Resistance, and most of the other characters take on their usual personalities, surprising that Silver isn't as naive as his previous appearances. Even Charmy makes an appearance, how fun. The secondary protagonist is the Avatar, AKA your OC. Completing various missions and stages will reward you with items to customize your character with and make him/her as unique (or terrifying) as possible, ask the Game Grumps how that went).
The main antagonist is Eggman, who brings back some of his old inventions, such as the Wrecking Ball Boss and the Egg Dragoon, it's even debatable if he died in the final fight or not. The secondary antagonist is who I originally thought to be Mephiles under the name of "Infinite". Infinite has to personally be one of my favorite new Sonic characters, his design is dark and brooding, he is incredibly arrogant and sadistic, to the point where he takes the series in a direction never seen before, with him slaughtering people on screen in front of us and the Avatar, showing how Sega truly intended for this to be the darkest Sonic game. Infinite's origins are both silly, standard, and interesting. He was once a mercenary who lead a squad of jackals to raid Eggman's base until he found out that he could have a chance to destroy the world, so he joined Eggman. Eventually his squad were murdered by Shadow, who kicked Infinite's ass with ease and called him weak, something that he seems to be insecure about, prompting him to take on the identity of Infinite. He is incredibly powerful, able to bend reality with his finalized Phantom Ruby prototype infused in his chest, he can also fly, teleport, and summon thousands of glitchy red cubes.
Sonic controls back how he did in Colors and Generations, as Sonic Team decided to bring back the boost feature and remove the drift feature. Classic Sonic has been reported as rather clunky, which I personally had no issue with, although I guess his speed declines a bit when stops after a spin dash. The Avatar plays much like Sonic, but instead uses gadgets to attack enemies, utilizing fire, lightning, cubes, and various other powers. The Avatar appeals most to be, and should also do so with fans, as having your character side with Sonic to stop Eggman shows how Sega cares about making their games as appealing to the fans as possible. The game also includes segments to take you out of the action and place it in more of a cutscene, allowing the player to home in on certain areas or just act as a mini cutscene.
Most of the stages in Forces can be completed in about 2-3 minutes, something which I believe was done on purpose for something in the future, although it makes replayability somewhat dull, as you can easily beat and memorize the layouts when you're not running through the level at high speeds or falling into pits. The boss battles are more challenging, well, not the first Eggman fights at least. Infinite will either stay stationary and charge at the avatar or stay ahead of Sonic and create cubes to kill him, his final fight can be compared to the Metal Sonic fight.
*Good level design.
*Simple and tense boss battles.
*Dark and gritty story with light elements.
*Intriguing elements of certain areas and characters.
*Infinite's backstory is rather weak.
*Stages can feel linear and dull after replaying.
*Tails' poor execution when encountering Chaos.
*Shadow's DLC doesn't allow the player to reply all of the regular stages (exception of 3).
*Fast paced action after mini cutscenes can lead to death.
*Stage 25 can be rather challenging without quick reactions, this can apply to all the other stages as well, but they are either easy to notice or not nearly as bad as Stage 25.
*The ending is only somewhat satisfying, Infinite's fate is unknown (hopefully he survives and realizes his wrongdoings) and Eggman still has around 0.01% of the world.
*Not too much replay ability after completion.
Overall this game earns a 7.4/10 for me, it may receive lower scores for most people, but not too underwhelming, surprisingly enough the website with the highest score is IGN, with a 6.9/10, which is pretty good. Don't believe anyone who says this game is among the worst Sonic games or is just as bad as 06, it's pure bullshit, because there are way more flaws in 06.
My suggestions for a sequel would be;
*Revealing Infinite's full backstory and making him a tragic villain which explains why he reacts so violently to being called weak, keeping him alive, and having him find redemption.
*Tying this into the IDW comics, which would make Neo Metal Sonic the main antagonist, so that the story of the sequel are the comics made into the games, which could make Tangle, Infinite, the Avatar, and Sonic the main protagonists, as well as including some other additional characters like Tails and Silver.
*Having Sonic fuse with the Phantom Ruby and becoming the final boss of the game after Metal's defeat, making him much more challenging than the Death Egg Robot and giving him the name "Phantom Sonic".
*Have Sega listen to the flaws the fans have pointed out and reworking and fixing them in future games.
*Potentially leave the game off on a cliffhanger with Infinte, setting up for a spin-off game with Infinite as the anti-hero protagonist (similar to Shadow the Hedgehog, but not terrible).
But these are just my thoughts, and I respect anyone who disagrees with me. Please let me know what else could be set up for a sequel and what you personally thought of the game.