Just as great as it was when it was on the GameCube, Mario Power Tennis is quite literally a smash.
For the most part, the new Wii Remote functionality works well. You'll move your character using the nunchuck analog, and swing your racket just like you would in a real tennis game (after all, that IS the point). No doubt you've played the Wii Sports tennis, so you'd have a pretty good idea of the mechanics of this game as well. Contrary to what some players might think of the new Wii Remote control, I believe it enhances the experience of an already great game, and totally worth the price of admission--especially for younger gamers.
Because this game is a GameCube port, don't expect any major graphical overhauls--not that it ever needed any since the game on its own looks fantastic. The only difference is that it makes liberal use of the widescreen format and, if you're playing this on a high-definition television, the game looks noticeably cleaner. Unfortunately, there's no online play for those who like that sort of thing. Still, if you've got local friends, you won't miss it much.
Overall, you can't go wrong with Mario Power Tennis--it's the perfect game for families and gamers looking for a fun and rewarding tennis experience with a pinch of Mario magic thrown right in.