Dragon Quest Heroes: Rocket Slime. Some may argue that its not exctly not well known, but its one of those games so called "hardcore" gamers won't play. It has the children-ish graphics, but hell its the DS why care about graphics, its gameplay is amazing. Its a Zelda-eque adventure game, but theres tank battles later in the game, which are awesome. Though it would have been awesome if there was wifi...
Then some I think are underrated: XG Blast, its actually a pretty cool shoot em' up sort of game, not really well known and I wouldn't know i if not for Hadrian's thread. Dokapon journey, a borad game RPG with pretty unique style. Henry Hatsworth, a cool hybrid between puzzle and action platformer.
This just my opinion but I think you should have a go.