So you can do lobs, drop shots, top spins and slices, but such precision is slightly undercut by the slow trajectory of the ball. Even Wii Tennis is much faster than this. Presumably the Power Shots are supposed to even things out, but even then these showy moves can easily be returned by a normal backhand from anyone with a modicum of skill.
Power Shots are different for each character and can only be unleashed by pushing the A button for a defense move or the B button for an attack - and only when your gauge has been charged by holding your remote up ready to strike. Defensive moves are obviously less aggressive than attack moves, which both happen in the form of cut-scenes (e.g. Donkey Kong fires his ball out a cannon, Shy Guy whacks it with a tribal spear and Daisy blows a powerful kiss).

Said cut-scenes cannot be skipped, although you CAN skip the action replays. That being said, did we really need them after every single point? Tournament mode offers you the choice of a regular match or a 'Gimmick Master' such as the aforementioned troublesome ghosts on court. These gimmicks are expanded upon for the Special Games mode, which is less about matches and more about hitting balls at paintings to colour them in or sending Bowser's bombs back toward his face. They're mini-games in disguise.
Finally, Exhibition Mode involves you taking off your clothes and playing in the nude...Oops, just kidding. It's basically there for you to enjoy a quick match instead of a long, drawn out tournament.

Mario Power Tennis is very playable but it isn't going to set your tennis world on fire unless you're a Mario completest - and if you are then you will already have the previous ports of this on the Gamecube or Game Boy Advance.