Thanks to Juri, I've recently had the chance to spend a half-hour or so with each of a bunch of imported Nintendo DS titles. As a result I'm able to give a quick run-down on where the fun is at, although my shortened experience with each and the fact I don't read Japanese prevents me from doing full reviews.
Daigasso Band Brothers: This game is absolute gold and I have no idea why it hasn't been Westernised yet. It's essentially a rhythm game where you're pressing the DS face buttons to play the music. The first gimmick is that you can play any instrument in any song; typically songs have six to ten instruments. The second gimmick is that you can play multiplayer with up to eight friends using only the one card, or with unlimited friends if they all have cards. Each player selects an instrument and together you play as a band.
The single player mode is decent but not special. However, playing with a full band is a one-of-a-kind experience. There's a fairly large list of songs drawing from anime, game themes, and Japanese and Western classics. Plus you can buy an expansion pack which plugs into the GBA port on the DS and roughly doubles the song list. If that's not enough, you can input your own songs, and the whole thing is remarkably friendly to those who don't read Japanese.
Doki Doki Majo Shinpan: The infamous "witch-touching" game turns out to be nowhere near as dubious or lurid as internet legend would have you believe. Although it's still pretty dubious. It turns out that one or more 14-year-olds at your local school may in fact be a witch, and it's up to you to stalk them like a creepy pervert and take photos of them doing incriminating things like, uh, saying hello to a cat (?).
Once you've amassed a weird little shrine of evidence, you can engage them in a battle, in which they'll throw fireballs or somesuch at you. Throwing fireballs apparently is not sufficient proof that they're a witch, because you'll then have to inspect their body for a witch mark. This is the "witch-touching" bit, and it's pretty rubbish; you merely have to tap on a still image until the witch changes pose, and repeat until her "witch mark" turns up. There's neither nudity nor ecchi involved. This is rubbish as hentai, rubbish as a traditional dating sim, and generally just a bad game. Plus there's more Japanese text than you can poke a stick at, so those who don't speak the language are going to be floundering.
Taiko no Tatsujin DS Touch de Dokodon: Aka Taiko Master DS, this is the DS port of Namco's successful arcade drum game. The bottom screen displays a traditional Japanese taiko drum, and the top screen has a scrolling list of drum beats. Red drumbeats require players to tap the face of the drum, while on blue drumbeats you need to tap outside the drum, symbolising striking it on the sides.
It's a bit watered down compared to the arcade machine but it's still a heap of fun, especially considering you can play four-player using only a single card. The song selection is a bit weak, with some classical offerings being the highlight, but this is still immensely recommendable to fans of rhythm games. You can play just fine without knowing the slightest bit of Japanese, too.
Meccha! Taiko no Tatsujin DS: 7tsu no Shima no Daibouken: Aka Taiko Master DS 2, it's the sequel to the first Taiko game. The main upgrade is a better song list, including such odd selections as the theme to SoulCalibur, so it's really less of a sequel than it is an expansion pack, I guess.
There's also apparently a story mode this time around although I didn't get to try that. The multiplayer is just as good as the first one, and once again you'll only need one card between four players.
Electroplankton: Strictly speaking you can buy this title in Australia, but it's the import version I played. It's just a collection of miniature game-like scenarios where you make interesting semi-musical sounds by interacting with the environment.
It's not musical enough to make actual songs, and it's not gamelike enough to actually have goals or progression, so while it's an interesting experiment it's unlikely to keep you occupied for more than thirty minutes total.
Oshare Majo: Love and Berry: Aka Fashionable Witches Love and Berry. This is a port of the Japanese arcade game. The original featured collectible bar-coded cards that you bought separately and swiped at the machine; each card depicted an item of clothing and by swiping the cards you unlocked that clothing for your in-game avatar. Core gameplay consisted of a dancing rhythm game where to beat your opponent you not only had to out-dance them but also be wearing a more stylish outfit.
The DS version keeps the card-swiping intact and even uses the same cards as the arcade, allowing for some portability in the unlikely event you live near one of the machines. The game comes with some basic cards but if you want more you're out of luck as they only sell from fairly rare dispensers inside Japan. It's a shame, because it's a reasonably decent game provided that fashionable witches are your thing.