While I was able to have fun with Tennis despite its limitations,
Yeah, I regret downloading tennis a little bit, but to be honest, it may be the best downloadable tennis game, dsiware or whatever, available on the 3DS. The mechanics are rock solid. The controls are super tight, if not a tiny bit unforgiving and, at times, a little too realistic. At first, it was really hard, I kept getting my butt handed to me on Level 1. And the way they work height into the game is crazy. Height of the ball in relation to the ground does matter somewhat and can affect how well you hit the ball, and you may sometimes miss, or even hit into the net. This is insane, of course, considering that this is a top down early Gameboy game, and completely in flat 2D. They represent height in the game by making the ball appear larger and smaller (larger means higher). But it's subtle, so it's very easy to misjudge the height of the ball.
Rallies can be very long and quite exhilerating, even at Level 1 difficulty, until you finally figure out the weakness in the AI. Now, don't get me wrong. The AI is pretty good. It's smart enough to do things like lob the ball high over your head if you get too brazen and stay close up to the net. The problem is that the AI is stupid, and consistently so, on the 2nd return when you serve, and on the 3rd return when it serves. Basically, in these situations, it seems like the AI fails to shift position towards center court if it's returned a hard drive toward a corner. Because it fails to shift, you can run up to the net after the AI has returned it and nail it into an opposite corner. I suspect this is an exploit. It is infinitely repeatable. Once you figure it out, Level 1 becomes a joke.
Then the game just gets worse, because Levels 2 through 4 don't seem to improve the AI or even vary the AI's play style. It's exactly the same. Only the frickin ball moves faster when both you and the AI hit it. That is the only change in difficulty.
So basically, it was fun for the hour it took me to really figure out the way the game works, how the controls work, how to judge the ball, and finally how to kill the AI. After that, I have no desire to play it. I doubt many people would.
So yeah, that was my very long (and slightly upset) way of saying "Yup, buddy, I completely agree with your sentiments."