While there are plenty of ways to freeze, electrocute or incinerate your rival, they all perform the same function - stopping him in his tracks. Similarly, each of the four hyperactive racers handles the same. There's no reason to choose Shadow over Silver at all, and their "unique" moves do little to make them feel like legitimately different characters. And while we're at it, isn't Silver supposed to be a whole lot slower than Sonic anyway?
The limited power-up system doesn't keep the action down, though. You'll never once be bored vaulting over logs onto different paths to overtake your opponent, or bouncing off his head to finish in first by nothing more than a hair's breadth. But, the same general issues the series can't shake are still present - namely, a huge amount of guesswork and unnecessary deaths.
Most of the time you're traveling so fast it's hard to see what's coming (made even worse by the PSP's usual screen blurring), so a trip or 10 into a bottomless pit is not matter of if, but when and how often. Why some areas are instant deaths and not just deterrents isn't clear either. Why would this river cause Sonic to die and the next merely slow him down? It makes snap judgments extremely hard to nail down. And as with other Sonic games, slowing down at all almost completely breaks the whole thing. These guys are built for speed, not careful jumping from floating platform to miniscule spring pad.