I may or may not be getting a 3DS

[Ayen]

Shin Megami Tensei IV
TheaterRyhthm
Devil Summoner Soul Hackers
Castlevania Lord of Shadows - Mirror of Fate
Etrian Odyssey Series
Harvest Moon franchise
Kid Icarus: Uprising
Kingdom Hearts: Dream Drop Distance
Kirby Triple Deluxe
Luigi's Mansion; Dark Moon
Monster Hunter 3
Professor Layton series
Project X Zone
Spirit Camera: The Cursed Memoir (Don't let the title fool you, this is a Fatal Frame spin-off)

Jesus...

I third Theatrhythm and also second the Professor Layton series - they are great games, I love them to bits. Even better, the 3DS is backwards compatible with DS games, so you can easily catch up.

I don't know if you have a DS or not, but even though it isn't technically a 3DS game, I would seriously consider getting The World Ends With You. It's a hidden gem, really.

I have a DS. Got it a couple of years back so I could play the first Phoenix Wright.