seangaffney posted an interesting list of his DS games and their respective completion levels, which I thought would be good to emulate. Therefore,
I give you my list of DS games, in no particular order
Electroplankton (Absurd Blue Import ver.) - 100%? A great demo for the DS' capabilities, but not much fun unless you are Toshi Iwai or similarly talented or obsessed with music. I've "played" all of it, but never got very good at making music.
Advance Wars: Dual Strike - 75% The gorgeous design and characters and the fast, addictive psuedo-strategy made this a must-finish game, so I did. I suppose I will eventually complete all of the special, side, secret, unlockable, and bonus missions to get all of the characters and background images.
Big Brain Academy - 30% Brain Age goes to college and becomes less intelligent due to alcohol poisoning, less interesting due to same.
Brain Age - 60% Still challenging and enjoyable, on the rare chance Noriko lets it out of her Sudoku-loving hands to let me play one board.
Clubhouse Games - 10% I got this so Noriko and I could play games together, but it languished when we got NSMB and Ouendan. I should at least unlock Chess, Go, and Shogi.
Freedom Wings - 100% Ultimately unsatisfying; think Strike Commander meets Warbirds for the Atari Lynx. When you can just fly around the engine is fairly impressive, given the DS' limited 3D chops, but fights are either annoyingly simple (grunts) or abusively hard (bosses) and the one other person who has it has already agreed, we're never playing it head-to-head.
Mario Kart DS - 100% One of the top 3 games for the system. If you don't have this, shut off your computer right now, go out, and get it this minute! Whenever we all whip out the DSes for a quick handheld game party this gets at least a few rounds, partly because it's great, but mainly because it supports 8 players from one cartridge. You'll want your own for the 20+ karts, mini-games, and instant wireless loadtime your own kart gets you.
MechAssault: Phantom War - 50% Absolute and unadulterated drek; I'll waste no more time on it.
Meteos - 50% The original, not the Disney re-brand. The offbeat setting and simple, yet deep, gameplay make this one I pick up every so often, although I never 'completed' the game.
Star Trek: Tactical Assault - 100% The name is almost ridiculously incorrect, as this is actually the tiniest condensate of Star Fleet Battles you can get in electronic form and not any kind of tactical game. A variety of missions, some slight amount of crew customization, and two story lines still only get you a game that appeals mainly to hard-core Trekkies... like me.
New Super Mario Bros. - 50% Unfortunately I had just beaten Super Mario 64 DS and SMB 3 (via Palm-based emulator) when this came out and I never finished it, but I picked it up as much to show Noriko the genius that a good Super Mario Brothers game could be as to play myself. I'll get back to it sooner or later, I think, since I'm about 50% through.
Trauma Center: Under The Knife - 6.66% I'll pick this one back up when I start hating myself full-time *and* I have copious free time. The difficulty curve shoots from 'piece of cake' to 'disarm a bomb in 3 seconds' level in around four missions. This is the only game so far to make me throw a stylus across the room.
Osu! Tatakae! Ouendan! - 50% Not much to say that hasn't been said, except that this is one of the cheapest ways to play rhythm games *and* hear top J-Pop hits of the '80s through today, and it kicks ass. Noriko is finishing off the Cheer Girls level in her spare time.
Kanji sono mama rakubiki jiten - ??% Not a game at all, but a sometimes-astounding, sometimes-annoying kanji dictionary. If I had just a smidge more kanji under my belt this would be a powerful tool... unfortunately Kanji sono mama is brutally unforgiving with regard to stroke order, so I can barely use it. A good English name might be "Kanji As They Be Writ", although I have to say that, if I were a native Japanese speaker or writer, it would be far more useful and worthwhile.
Rumble! Custom Robo (import via 1/2price used soft store) - 98% Kind of Virtua On for the Pokemon Generation, Custom Robo (I think it's Custom Robo Arena here) has just the right balance of story, fighting, grinding, side quests, and customization. Nothing stands out as exemplary, nothing I can recall made it unenjoyable; it's a light, fluffy package of robot combat RPG-ish fun. I hear the American translation was butchered like Sweeney Todd's clientele, though. (The last 2% are two robots I would only be able to get if I went back in time to Christmas 2006 and downloaded them from a DS demo station in Japan).
Shikakui Atama wo Maruku Suru - 0% A Japanese quiz game I bought at the aformentioned 1/2price software place in Japan in a fit of unmeasurable optimism. Noriko played it for 10 minutes before declaring it too easy; I played it for 10 seconds before going back to Custom Robo.
Sim City DS (used import) - 1% I *guess* it's an admirable attempt at porting SC3K to a hand-held, but considering that you could run SC2K on a 33MHz Mac LCII, and that the N64 version of SC2K was fully 3D, there doesn't seem to be any reason *or* excuse for the lack of features or fun here.
Jump Super Stars (import) - 70~80% A lot of fun, and good for pickup download games, JSS does suffer from a few design flaws, mainly in the Koma collection and unlocking system. I'll never complete it because Jump Ultimate Stars basically fixed all JSS' issues, added more characters, and also has 'Ultimate' instead of 'Super' in its name.
Daigassou! Band Brothers (import) - 25% Pre-Jam Session, post Rhythm Tengoku, it's a rhythm game-cum-sequencer that I would have beaten by now but I thought I'd lost the cartridge! Imagine my surprise when, just now, I opened the box and found the pristine cartridge inside.
Chou Soujuu Mecha MG (import) - 99% There are 120 unlockable mechs in this *fantastic* game from Japanese mini-developer Sandlot (of The Earth Defense Force and Robot Alchemic Drive, etc.) and I have all but two. I have also surpassed the displayable play-time limit... of 999.99 hours! This is my #1 most-beloved DS game; I could lose all the rest in a fire and I'd be okay so long as I still had Chou Soujuu. I'm totally serious.
Picross DS (import) - 33% This exemplifies 'casual', but at the same time it can be so engrossing and challenging I kill an hour or two without even realizing it. Everyone should have Picross, if only for those times when they are tired of other games or when a niece or nephew needs to be kept occupied.
Front Mission 1st (import) - 25%, maybe? This super-uber-ultimate-extreme port of a port of a remake is about as good as non-Final Fantasy tactical combat gets on the DS, which is ironic because the game's by Enix and the characters are by Amano. It's sort of Battletech meets FF:Tactics and they decide to be the surrogate for Metal Gear Solid's baby clone, but tailored for people who min-max their WoW gear. Recommended.
Legend of Zelda: The Phantom Hourglass (import) - 90% I doubt that any game before or since has utilized the DS as a medium as well as Zelda did. The story was simple and the dungeons weren't all that challenging, but it was so brilliantly executed I never noticed. The remaining 10% represents side quests I decided to save for a rainy day. Also, selectable kanji readings ftw!
Super Robot Taisen W (import) - 50% Some of the best crossover giant robot fanfiction I've ever played, and an example in the correct use of original characters. I got burned out right around the boss fight that separates the first and second halves, but I will *definitely* go back to find out what happens next, probably as soon as I finish Front Mission. The original characters alone are worth the price of admission.
Worms: Open Warfare 2 - 100% Short, amusing, nostalgic; it's hard to describe a game that marries cartoonish talking worm soldiers with Scorched Earth any better than I just did. It seems that the world is split about 10/90 for/against this game, but I've got mine so nyah.
Glory Days 2 - 100% Another nostalgia game, this time based on Chopper Command and Choplifter. The pro-war tone of the supporting cutscenes is strange coming from a French game, but I was able to get past it to enjoy the bombing and building.
Geometry Wars: Galaxies - 60~70% I doubt anyone has *not* heard of Geometry Wars. This incarnation gives up some of the hyperfidelity of the 360 XBLA version for rock-solid controls and a sort of tidal rhythm that can put you into a trance of dodging, shooting, and geom collecting faster than you can say, "Ommmmmmygod, a black hole!" The new drones are a nice addition.
Super Mario 64 DS - 100% The definitive N64-to-DS port. If you haven't finished the original (as I had not) or if you want an exuberant 3D platformer with mini-games and an amazing world that you can explore at a moment's notice, get this game. I think it's been out of print for going on three years, but it's well worth tracking down. Hopefully it will be joined by a Galaxy incarnation in the near future, but if not, we'll always have Peach's Castle.
Honorable mention: Rhythm Tengoku (import) - 100% From the minds that brought you Wario Ware: Smooth Moves, among others, this is a GBA game that is almost too perfect to exist. Each level is maybe a minute long, but all told there are hours of gameplay and joyful tiny characters to experience - and that's not including the full drum kit studio!
Whew, that's a lot!