Split/second is a mixed bag, mostly good
In short, Split/second isn't a hard game to rate. It's really straightforward: a decently fun racing game with a main sell --power plays. Power plays can range from downright useful to extremely over-the-top explosions that decimate an entire chunk of a city (which effectively changes the racing route). Driving through intense sequences desperately trying to stay afloat while simultaneously attempting to crush your enemies. This is where the game shines its brightest.
Still, however, the game is definitely not without its flaws. For one thing, because the game relies so heavily on one gimmick, it doesn't have the greatest half-life. Also, the races can be rather unforgiving. Just imagine the exact opposite of a game like MarioKart, where you can always recover no matter how far behind you are. In split/second, if you aren't consistent with the sometimes-overly-harsh AI, you can lose all hope whatsoever mid-race. This is made even more extreme by the fact that no matter how many 'awesome' cars you unlock, the cpu will always be two steps ahead of you regardless.
All in all, pretty fun game. Nothing groundbreaking, but if the situation calls for, it has the potential to be right on the money.