It depends on what kind of game you like. For me, there's a lot of games worth of having a 3DS (im a handheld console guy, so i love the 3DS)
Some examples are Shin Megami Tensei 4 and 4 Apocalypse, excellent jrpg games, and 3DS exclusives. Also, if you are a DQ fan, the 3DS its a great console, with the remake of DQVII, DQVIII port, DQTNW, DQXI, DQMJ3, etc. And i really enjoyed Xenoblade Chronicles 3D. Its not the best version of the game (there's the original on Wii and the remake on Switch) but it is a blast for me to play it on a "real portable console".
Aside from that there's a couple of games i enjoy that are 3DS exclusives: Luigi's Mansion Dark Moon, Kid Icarus: Uprising, Ever Oasis, Yo-Kai Watch 1, 2 & 3, Monster Hunter Stories, Persona Q: Shadow of the Labyrinth, Shingeki no Kyojin 2: Mirai no Zahyou, Beyond the Labyrinth, E.X. Troopers, Dead or Alive: Dimensions, Dragon Ball Heroes: Ultimate Mission X, Boxboy 1, 2 & 3, Dinasty Warriors VS, Fire Emblem Awakening, FE Shadows Echoes of Valentia, Dragon Ball Fusions, Dillon's Dead Heat Breakers, Castlevania LOS Mirror of Fate, Kindom Hearts DDD, Super Mario 3D Land, Kirby Triple Deluxe and Planet Robobot, Bravely Default and Bravely Second.
Honorable mentions (because were ported to other plataforms, are a port from other consoles or a remake, but are great on 3DS): Resident Evil: Revelations, Alliance Alive, Code of Princess, The Snack World: Trejearers, Hyrule Warriors Legends (all ported to Switch), Nightsky, Luigi's Mansion 1, Terraria, TLOZ Ocarina of Time 3D & Majora's Mask 3D, Spider-Man: Edge of Time, Shovel Knight.