I would love to give an in-depth review of this film but Google can be a bit funny about it, so I'll keep it as short and informative as possible.
The trailers exclusively used the best elements of this film to trick people into thinking it would be a more mature, action-packed, emotional ride than the previous two films. Instead it was 90% Jim Carrey making a fool of himself while hedgehogs uncomfortably watched. it's clear that the writers had no interest whatsoever in the franchise they were trying to represent. Instead, all their effort went towards making Jim Carrey as "funny" as possible.
The story is supposed to reflect the story of SA2, but this film feels so utterly disconnected from the source material that I struggle to make sense of what's even happening.
Shadow is reduced to an emo stereotype who does nothing but talk about pain (the "Hot Topic" comment made towards him says a lot about the way the writers viewed him..). It would've been nice to see Shadow smile or seem remotely happy while he was with Maria, as that would've communicated how trauma effected his identity after the Ark incident. Character development is a rare nectar in corporate films, unfortunately. Shadow hardly got the screen-time we expected, which was awful because HE'S the character everybody paid to see. That said, Keanu Reeves was cast for the marketing value, so maybe it was for the best.
Gerald shouldn't exist in the first place because he was executed in the original game's story; so not only did they bring him back as an excuse to give Jim Carrey more screen-time, but they butchered his characterisation too. Gerald was never a villain. Shadow Generations blessed us with his journal (thank you, Ian Flynn), expanding on his character and showing us the series of events which lead to his downfall. He's tragic. sympathetic. Kind. This movie presents him as a washed up lunatic with no compassion for anybody at the ripe old age of "110". Disappointing and embarrassing.
Maria's actor was not only a poor casting choice, but she didn't portray the character appropriately. Maria is supposed to be delicate, softly spoken and emotionally mature for her age due to her suffering the game's equivalent of AIDS (a feature they removed in the film, which defeats the point of shadow's existence as he was created in search of a cure). Instead, she's a typical boystrous child who causes chaos and sees everything as a game.
Sonic is eye-scratchingly annoying to watch and listen to. scenes involving him, Tails and Knuckles are mundane and drag on without any real substance. Also, forgettable human characters exist once again.
This film repeatedly references other IP's (Hello Kitty, Pokemon, etc) and there's no way they weren't sponsored.
I could fill a book with the amount of issues I have with this film, but I'm gonna stop here.
You know a movie's bad when your theatre is packed full of kids and they're dead silent through the length of the film - minus the first 5 minutes. This film goes WAY too hard on the "comedy" aspect, yet the only people I ever heard laughing were the adults; and mainly at the pop-culture references and odd few lines of dialog that actually felt remotely witty. it might just be that British children are more cynical and harder to please than American kids, but whatever.
This film makes a mockery of SA2's legacy and I do not recommend watching if you're a respectable sonic fan.