Mine has to be Dragon Quest: Rocket Slime, a DS spin off of the Dragon Quest series that sees you playing as a slime operating a tank and rescuing the people from your town. You run around the overworld, collecting items to use as ammunition and saving money to upgrade your tank. The art and music are just as great as you’d expect from the Dragon Quest series. It made fantastic use of the DS’s dual screens. It’s also written for a younger audience, so a lot of it is just really silly and fun! Try it out for sure, I’m so sad there’s no sequel :(
Not much nostalgia for Jet Force Gemini, a Rare third person shooter where you adventure through missions, each having secret routes to find using guns/keys you slowly unlock. The game had a bit too much completionist vibe to get to finish it, but was exciting as a kid.
On the 3DS, I also liked Resident Evil: The Mercenaries 3D. Basically RE’s best arena mode expanded out with perks on a game you could play mobile, and online. I still hope to see more of that type of experience.