A third Sonic film rolls off the production line with remorseless inevitability, and no little excitement among its core early-teen fanbase; the Marvel Cinematic Universe could take a lesson or two in how to keep the audience onside. The kerfuffle over Sonics weirdly designed teeth seems a long time ago and if Jim Carrey is really only in it for the money, he certainly gives his double role here some major welly. And while no one could deny the cash-grab fan-service underpinning to the entire project well, its actually a not unenjoyable experience, even if you are someone on whom the intricacies of early-00s game narrative are lost.So this Sonic reboot takes the time-hallowed third-instalment approach by foregrounding a dark version of Sonic in fact near-identical hedgehog Shadow, distinguished from our hero by his black and red colouring. At the start of proceedings, Shadow escapes from a containment unit where he is being held for various convoluted reasons, and Sonic (along with his echidna and fox sidekicks) is called in to deal with him. Pretty soon, for further convoluted reasons, they briefly find themselves fighting alongside Ivo Robotnik before and I dont think this is a major spoiler unearthing Robotnik grand-pre in an abandoned military base. Then it starts getting complicated.Having a rich stew of plotlines, character arcs and dramatic incident to draw on from more than three decades of games means that this film is, frankly, groaning at the seams with switchback story-moments, seemingly random flashbacks (often unannounced) and bizarre sideways leaps; but its all held together, just about, by a kind of delirious energy that creates its own momentum. The human elements are a bit hit and miss: the big name voices from Keanu Reeves and Idris Elba (as Shadow and Knuckles respectively) arent knocking anyones socks off, and James Marsden and Tika Sumpter (as Sonics adopted family the Wachowskis) are a chemistry-free zone, looking like they met for the first time seconds before the cameras started rolling. Carrey, though, is very good value, getting off a couple of lines that might actually make grownups laugh, and generally putting himself about to decent effect. Without him, this film could have been a lot, lot worse.