My first 3DS game was OOT 3D. Despite the fact that technology has dramatically advanced over the years, I still find it surprising that a handheld system's hardware surpasses a home console (in this case it's the 3DS having superior hardware to the N64).

Does demos count? If yes, KH:DDD' démo, if not, Kid Icarus Uprising.

Mine would be Pilotwings Resort.

Super mario 3d land I have red 3ds :)

Sad to announce Virtue's Last Reward was my first, sad because it's hard to play anything else after that, er

Wow, Virtue's Last Reward? That's the sequel to one of my favorite DS games, 999. (Nine Persons, Nine Doors, Nine Hours.) Did you know that, in Japan, that, roughly translated, means Good People Die?

Tom Clancy's Splinter Cell
... I had to share the 3DS with my brother, and he wanted that game, so we got it