This game should come with every new DS sold!
The mechanics are simple. The graphics are simple. The music is simple. And this is simply one of the most fun games I've ever played.
The fun comes from the combination of music, animation, and the rhythmic tapping, holding, and flicking of your stylus in time with the music. Rhythm Heaven presents a series of rhythm games to challenge you, and as you progress you'll unlock more rhythm games, so there's always that carrot dangling in front of you, pushing you to keep going. Even when you've made it through all the rhythm games, there's still more to do. You can go back to games you've already completed and try to get a Superb score, which is done by completing each rhythm game with only one or two minor flubs. For this you're rewarded with medals. The medals unlock mini games and other goodies to play with. And, for those completionists out there, occasionally the game challenges you to get a perfect score on a rhythm game. Successfully perfecting a rhythm game is very rewarding in itself, and also unlock more goodies for you to play with.
But the best part of the game is the music. It's simple and catchy and I found myself singing the songs when I wasn't playing. Also, the simple tap-flick-hold game mechanic makes it super-approachable to kids, adults, casual gamers and hardcore gamers alike. I think everyone will find something to like about this game. Now, that's not to say the game is easy; there's enough challenge that I doubt I'll ever get a perfect score for every rhythm game. But it does mean that I think everyone should play this game because I think everyone will like it.
The only possible down-side I can think of is that Rhythm Heaven doesn't make a great mobile game; at least not for me. The game requires you to have the sound up to play, which can be awkward. Even if you wear headphones you'll be tapping on the DS screen and that makes noise. And, the intensity of the rhythm games can be a bit much for public situations; some of the rhythm games require intense concentration. But that shouldn't stop anyone from getting the game. Just play a different game while you're one the plane, on the bus, in the car, or wherever, and save Rhythm Heaven for when you get to the hotel.
I feel that everyone who owns a DS should own this game. Like Super Mario Bros on NES, or Halo on Xbox, this game screams DS and will forever be one of the first games I think of when someone asks me what game they should get.