First off, the acceleration is clunky and unrealistic. When you hold down the accelerate button to reach the maximum speed, this speed is actually reached within the very first second of acceleration. And then when you stop holding down the accelerate button, you come to an almost instantaneous stop. This game is probably the first racing game that I've seen that lacks simple graded acceleration/deceleration physics. Sure, there's areas with mud that slow you down, but that's about the extent of it.
In addition to that, and if that wasn't bad enough, no matter which gender/bike speed you pick, the speeds are identical across the board. Now, this might have been acceptable in some older games, but racing games these days make use of different vehicles and whatnot with varying strengths and weaknesses. This adds a bit of depth to the game and forces you to adapt to different tracks based on the vehicle that you're using. Not so in Platinum. Here, both genders are equal to the other and choosing one comes down to merely an aesthetic preference, while the bike gives you two speed choice: fast and faster. Not a lot of variety.
The game is also an example of how innovation can go bad. The track design, while undeniably innovative, is also the worst that I've seen in any game. The tracks are riddled with really annoying **** tacked on for the sake of being the first game series to implement the gimmick. Case in point: track obstacles that range from obtrusive foliage, ledges and buildings, to annoying monsters that attack you in order to distract you. The tracks are also convoluted to the point of being more like mazes than anything else, and the twists and turns of the tracks can sometimes be so abrupt as to come to a ******* 90 degree angle. I should mention that you can pick up these little monsters in order to help get past the random ones that pop up, but they're still a major distraction and slow you down too much.
tl;dr: I haven't played any of the others, but if Platinum is any indication, this is one racing series to stay the **** away from.