My biggest issue with the DS is that a lot of games try too hard to take advantage of all the features, and wind up being clunky as a result. For example, the Metroid game that wants to use the stylus for steering and the console buttons for actions, or a mini-game in Cory in the House that uses the stylus to steer, the up button to shoot, and the left shoulder button to brake - the controls are just awkward. Even Phantom Hourglass got into it a bit with the “spin attack” requiring a specific stylus movement to activate.
That said, there are some really good DS games (Phantom Hourglass being one of them, spin attack issues aside). Some are surprisingly in-depth, such as Phantom Hourglass and Hotel Dusk.
Phantom Hourglass is good, but gets a bit repetitive; you’ll have to do the same dungeon areas several times, repeating the puzzles to progress. There are also some “secrets” that are a little too-well hidden and require either going over every area with a fine-toothed comb, or using a guide if you’re a completionist. That aside, it’s entertaining and offers several hours of gameplay.
Elite Beat Agents is kinda cute and entertaining, but can also get annoying and ridiculously hard after a while.
Advance Wars is a challenging strategy game, with fairly good AI from the bit I played, offering some replayability due to changes in AI response. I’d recommend Days of Ruin for a more realistic feel than Dual Strike.
Trauma Center is cool, but gets a little silly at times, and is another one I found the stylus movements were odd and frequently didn’t register properly.
Mario Kart is a hoot if you have a couple other people to play with (and screw over, hehe) some time; just be sure to practise and unlock some of the better vehicles.
The Castlevania games are fun for the genre, but sometimes require some difficult movements (jump combos), so can be frustrating if you aren’t “good” at arcade style games. They can still be very absorbing and offer hours of gameplay.
The hardest DS game I played was one I can’t remember the name of; it looked like an elementary school kid’s puzzle game based on Pokeman with silly minigames and card games, but the minigames were frequently extremely difficult to the point I was unable to complete them. I guess you have to be 8 to be able to win on that one.