Some comments on games mentioned so far:
The World Ends With You - The reason I haven't played this game yet is that I haven't liked any games Square has made since the SNES, except for the FFT games. RPGs for me come down to two extremely important factors - pacing, and character customization. Does TWEWY move quickly and have a lot of options for tweaking how I play the game? If "yes" to both things, I will strongly consider TWEWY.
Ghost Trick - I don't need to be sold on this very hard, I'm probably going to look into getting it soon.
Mega Man Zero COllection - I already own all four MMZ titles on the GBA, so I don't think there's any particular reason to own this, unless I get it like really cheap or something.
Last Window - This is a game I really want, but I'm not sure if it's worth the elevated price tag. If I really liked Hotel Dusk, should I just bite the bullet anyway?
999 - Is it a pretty sure bet that someone who loved PW and liked Hotel DUsk will like this? I'm still a little on the fence here, because it's actually really unusual that story-driven, "visual novel" games appeal to me. PW and Hotel Dusk did, though.
Anything with Dragon Quest in the name: Same RPG rules apply. Pacing and customization?
Anything with SMT in the name: Pacing and customization again, also are they worth playing even if I have absolutely no clue about the rest of the series? I've never played them.
Radiant Historia and other RPGs I know nothing about: Pacing/customization? Does it move fast and have a lot of ways to tweak my characters?
Pretty much everything else named so far I haven't even heard of, so I'll have to do a little bit of research and find out what they're like, but so far I like the number of unusual suggestions coming in.