may i suggest the Gameloft DSi games?
no clue why but Gameloft ported a decent amount of their J2ME games to the DSi, and the games they've ported are actually pretty fun! Soul of Darkness, Hero of Sparta, their quality is all over the place but i found stuff like Gangstar 2 to be a fun take on the 2D GTAs.
there is a lot of good 3DS stuff that hasn't mentioned on the thread either.
the River City series - also called Kunio-kun - got some entries on the 3DS, Rival Showdown and Tokyo Rumble are both pretty fun games, they feel like extensions of the original NES game, SMT IV is the best game in the whole series but there's also Soul Hackers, Strange Journey Redux - recommending this for people like me who's 3ds cant run the DS Strange Journey without it running at 12 FPS for some reason. - , the Persona Q games are really nice dungeon crawlers, especially if you are a fan of the Etrian Oddysey series since they are based on those games.
As for the DS, Tetris DS is one of the best takes on Tetris, so much that i tend to return to it every now and then, the Plants vs Zombies DS port is worth checking out for the exclusive stuff on it, the Retro Game Challenge series is amazing - the second game being Japan-only, having an english patch. -, Blue Dragon has art made by Akira Toriyama, the Castlevania DS games are all amazing, Dragon Ball: Attack of the Saiyans is a really good RPG, the FINAL FANTASY DS games are all pretty great, Meteos is one of the greatest puzzle games ever created and i heard some pretty good things about Solatorobo.