Bumping for the benefit of new readers...
I haven't found Nintendo's first-party stuff particularly enticing, to be honest. I can second Phoenix Wright, Advance Wars and Trauma Center; they're good, although Trauma Center is kind of difficult.
If you like 2D scrollers, Mega Man ZX might be your thing; it's also kind of difficult (in a good way), though.
My suggestion: Import, import, import. You won't look back. There are plenty of online stores out there which do import games.
Band Brothers (not to be confused with Band of Brothers) - Brilliant rhythm game. I don't consider myself a rhythm gamer per se, but 2 of the best games on the platform are rhythm games, and this is one of them. Better yet, get a couple of DS-owning friends to import as well, and get together to jam. Japanese proficiency is helpful when reading the menus, but you can pick up a translation guide at GameFAQs.
Ouendan (Cheer Squad) - The other rhythm game. Also amazingly sweet and lots of fun. Doesn't require (much) language proficiency, and I'm almost certain a translation guide is out there.
Chousoujuu Mecha MG - Best use of touchscreen since Trauma Center; think of it as a mashup of Wario Ware and Mechwarrior. Interested? The premise is that you pilot these giant robots, which are apparently inspired by old-school toys (think the first-generation Transformers and other stuff of approximately that vintage). The hook: most of the robots are controlled via the touchscreen. The D-pad moves the robot forward, back and turns; it's also used to jump (via double-tapping) and guard. Each robot, however, has a unique control panel (displayed on the touchscreen) with levers and dials, etc. Some of these are incredibly creative - for instance, the Hatman's torso and arms are controlled via a marionette-like handle with strings attached, whilst "archer"-class robots require you to pull back a bowstring and release it to shoot, and "gunner"-class robots generally require you to cock the weapon, either by moving a hammer or pulling back a charging lever, before pulling the trigger to shoot. It seems to need some Japanese proficiency (primarily for mission objectives), but it's usually possible to figure things out just by messing around. The story isn't exactly Booker Prize material, either, so you won't miss much. I'm currently playing this; it appears to be pitched at the kid market and toy nostalgics, but it's tons of fun.
