A couple of annoying things that have become apparent, the more I've played the game:
1) Side-swiping opponents really screws with your handling, so it's risky to use. I side-swiped a character, right before a jump, and it made me veer far-enough to the left, to make me jump clear off the track. I got hurt more than the guy I swiped. It seems like too much of a risk, considering how hard it is to perform, in the first place. The chance of you crashing, or losing speed, is greater than the chance of it helping you. I only really use it, if I'm on a straightaway, or if it's required for a goal. Otherwise, the risk outweighs the reward of stalling your opponent for a short moment, and gaining a little boost meter.
2) I hate that you can't customize the controls. It limits my ability to use all the buttons, in the most effective manner. For example, I'm constantly drifting whenever I can, which makes it hard to swipe opponents, fire weapons, or use my shield, since it requires me to release the drift button. Sometimes, I'll be sliding right alongside another kart, and I can't swipe them, since my right thumb is stuck holding the drift. Mapping the drift function to a shoulder button would fix that. Another example, is I'll be performing an air spin, and a weapon starts homing-in on me, mid-spin. I release the right stick, to activate my shield, and I end up not completing the spin, and land backwards or worse. Mapping the shield function to a shoulder button would fix that, too.
That said, I still love the game. I only have a couple more races to beat, on the last tour. Though I have about a dozen goals and severals grudge matches to complete. I just wish my wife wouldn't hog it for 2 hours, straight, trying to make her mod as cute as possible. :lol