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 :(
Planetside 2 - someone else already mentioned it here, but it’s the only game in it’s genre and nothing else really comes close to what it offers (persistent 1v1v1 +300 player battles across infantry, land, air, and sea). It’s been kicking for over a decade now and I’m not sure what could replace it if or when it finally kicks it. It’s truly singular, and responsible for some of my fondest memories in gaming. It’s also free!