i was originally gonna write a long post about why this is my favourite console despite (and because of) its foibles, but instead i'm just gonna be standard here and say: good damn console.
neat gimmicky experiments and solid games mixing and mingling together to form a weird era of game design that carried over the spirit of the GBA by combining 4th-7th gen game design aspects into a melange that can only be described as "nintendo ds :)"
mine is Dragon Quest Heroes: Rocketslime
My gut instinct is to say the Mega Man Zero Collection (2010), but that's cheating since it barely adds anything to the 4 GBA games it's a compilation of... so instead I'll go with a game I actually didn't get around to beating until some years after I originally got it, which is Kirby Squeak Squad! Really fun game, and I got it roughly around when it came out (probably not at launch, but definitely while it was still in stores), but I didn't actually get around to playing it more seriously until sometime in high school (sophomore or junior year I think, so around 2013-2014?). I wound up 100%ing the main story mode, if memory serves, though I didn't finish the speedrun mode where you're supposed to grab all the treasure in a single sitting (or whatever that mode's goal was). I loved the element system for the copy abilities, even if I wished they'd gone more in-depth with it (or at least let it apply to more abilities), and the way they implemented Ninja in that game was really fun IMO. Also, as someone who adored the sprites in Nightmare in Dream Land and Amazing Mirror, I was really really glad they kept that visual style for Squeak Squad. Love me some good "Kirby Advance"-style sprites, mmm 👌