I have 14 of these 20 games. Here are the 6 I don't have:
Persona Q (interested in the genre but have not played Persona 3 or 4 yet so would be clueless about the characters)
Donkey Kong Country Returns 3D (have it on Wii so no reason to get this)
Shantae and the Pirate's Curse (not interested)
Mutant Mudds (tried the demo, not interested)
Pokémon Omega Ruby/Alpha Sapphire (somewhat curious, might get if cheap)
Shovel Knight (not interested)
You asked for it, you got it!
If you hadn't then I would have.
I just bought Theatrhythm: Curtain Call. Not sure I'll like it as the demo never wowed me from the first Theatrhythm and I've played no Final Fantasy games so I have no connection to the music.
Just make sure that you use headphones or some sort of external speakers, as the music has some nuances that you just won't hear on the tinny 3DS speakers.