There's probably a lot more, but this is just what came to mind first. Also worth remembering that if you hack it (and you should if you haven't, it's pretty easy and the eShop is gone anyway) then you can natively play original DS and GBA games as well
the Ridge Racer game is pretty good, if you're into visual novel-esque games I heavily recommend Virtue's Last Reward. EDGE is also a good time waster.
Dittoing Crab's recommendation of Fire Emblem Awakening - for nostalgic reasons it's probably my favorite in the series, but even without that it's still a great game. The series spent forever chasing after excuses to re-implement its mechanics for a good reason.
I'm a huge fan of most rhythm games on the 3DS so like, Project mirai, Taiko, Rhythm thief and Rhythm paradise megamix nstuff. Of course the monster hunter games I think are really good and its got imo the best version of Animal Crossing which is New Leaf.
ahhh i wish i could get into New Horizons the way i still bump New Leaf. there are some improvements in NH that are annoyingly missing in NL, like how balloons can drop on paths (going back to NL and seeing every balloon disappear because the surface area of my town is 70% flowers and 20% paths makes me want to cry)