Have now reached 50 and still playing games. I love the DS because you can pick it up for just 5 minutes where ever you are.
Had this on the original N64 and thought it was good then. Transforms to the DS well and is a lot better than 90% of the new games out there.
Control is fairly easy and soon mastered after a bit of practice - there is various ways to control the charactors. Some of the other comment may not have noticed. I used the stlus on the lower screen to guide the charactor and press the buttons to jumpand flip, etc. You will watch the charactor on the top screen and his control becomes second nature and you ignore the lower map/control screen.
Basically you are tring to collect 130 odd stars from strange room/worlds. You gradually unlock more rooms as you collect enough stars. Things get gradually more harder and you learn new charactor movements to help in this. You develop these skills as you progress in the game.
Some stars require Mario's friends to get them and they have to be unlocked by defeating some baddies.
Some stars are easier to get than others - if you get frustrated in one area you can go to another room to do something different.
Look on the internet and you will find some walkthroughs for advice. Its surprising wot secrets that you can miss and there is lots of them.
If you are an older player then ignor the cover picture this is a challenging game that will keep you entertained for hours.