It will make you come back for more...out of frustration
The 'standard' game, in which you are playing on various court types (grass/clay/hard) keeps you interested, even if the difficult is a bit out of whack when you hit the third cup - the two cups before are relatively easy. But that's quite minor - as your skills improve you get used to how the computer plays.
You *can* use the nunchuk to control your character, but without it the running around is done by the software which makes it much easier to set up your shots, which do need practice to execute properly (with some characters easier to use than others). I'd avoid it until you actually want the additional challenge of controlling your player's movement on the court.
I'm in two minds about power shots. They're cool, but when you do manage to execute an awesome shot, all that effort gets negated by the opponent pulling out their power shot and it's back to square 1. They remove some of the skill, and I've found it best to keep mine 'stored' to simply negate my opponents.
I've found it addictive, but not Mario Kart Wii addictive. I find Mario tennis a step up from Wii Sports Tennis, but the largely irrelevant mini-games and infrequently dubious controls make this a good but not great game.
Get it, but be prepared to put some work into it. If you do, you can spend many an hour on the courts...