Is this worth picking up?

This is the first Mario Tennis I ever played, but so far I can't say I enjoy it as much as I want to. The characters don't have any special shots, like they do in "Mario Sports Mix". Instead, there are five different kind of shots.
If your oponent makes a bad return, a circle pop up at the ball's landing spot. If you use the correct shot, you'll give the ball some extra power. Better than nothing, I guess.
Oh, and if you press X, you'll use the best suited shot for the moment, the onmly downside is, that this shot is a bit weaker.

The controls... well, there's regular way of playing and the Gyro-Sensor.
The regular play... well, overhead view, move the character as you please. Though I have a hard time guessing where the ball will land on harder difficulties. But it's perfect for the minigames.
The Gyro... well, the character moves on its own towards the ball. Not bad on harder difficulties. But the aiming is odd, as you need to "aim" by moving your 3DS to the left or right. I don't like that very much and think aiming is a bit harder that way. You can still move the character on your own, if you like.

Now as for online, that's something to watch out for. Most online players use their Mii or Boo. During the times I played online, I only saw one other character. And they probably use the Gyro as well.
Now, the advantage of playing as your Mii is, that you can costumise it to your hearts content. Depending of what outfits you equip itr with, its stats will alter. That way, you can make a very strong character. And as far as I can tell you, that's the only way to give your oponents a proper challenge, as they'd destroy you otherwise. But if you're properly prepared, online is fun. And if your oponent is a monster, keep on fighting, don't give him an easy win.
Also, Tiebreak-Mathes seem to be the most popular, at least in Europe. You only need 7 points to win a match.

Oh, and no items either. That's a real bummer for me.
I also find solo play to be... lacking. You have four minigames which you can play to collect coins. Those are needed to buy outfits for your Mii.
Also, there are only four "unlockable" characters, all for beating the third level of every minigame.
There are also more secret characters. Yoshi. In different colours. Uhm... yeah. You need a QR Code to unlock them.
And you can still try to make every character a star player. All you need to do is to beat the Champion Cup. And only that.
Oh, secret characters won't appear in tournaments, unless you play as them. There's also a proper offline Versus.

To be honest, it's not a bad game. I wouldn't call it "good" either, though. It's somewhere in the middle.