Diner Dash for the Nintendo DS is a fun, challenging game. You can play a Career track, which follows Flo through different restaurants, Endless Shift, where you play until you lose five tables, and multi-player, which is done with another DS-wielding player.
The graphics are bright and clear, the characters have personalities, and the music isn't too bad. I find the gameplay to be somewhat difficult, and I've had to play several levels over and over again before I beat them -- and I'm almost 21. This would be a good game for a kid or an adult.
The one unnecessary detail is probably the "customizing" of the restaurant after you complete a level -- you're given the choice to pick between floor and table colors, pillar and door style, etc. While it's cute, your choices don't actually have any real impact on the customers. There's no wrong decision.
I give Diner Dash a five for fun. Because it follows a very loose storyline, I'd also give it high marks for replayability. It's addictive, though -- so be warned!