Mario Tennis is only ok. I like the way it looks, the stages, etc. But the cut scenes are fucking ridiculous everytime you use a power shot. I mean, it's an atrocious gameplay killer. The thing is, the game is very vanilla without the strategy of using super shots, so it's either play a gutted game or sit through a HORRID decision every time you use them. I can't stress enough how it hurts the game flow. The single player is barren and the mini-games are beyond dumb. I like the Nintendo "feel" in some of the controls, but the downsides are really painful for a $50 game. Should have been sooooo much better.
It's true that you can use your special power ups to get to balls that are past you...but that didn't bother me so much since your timing in using them is somewhat strategic. If you can live through seeing the same retarded power up scene past a few hours, you may have far less gripes than myself.
I'd suggest Top Spin at the price point. Rent both, I'd bet my life you'd agree.
I still play the demo every once in a while to marvel at the ball physics, which are unmatched among tennis games.