If I have to pick just one, as per the OP, it would have to be Monolith Soft's "
X." My reason is this
trailer. I also absolutely adored Xenoblade Chronicles; I found it one of the very best games of last generation. No matter how closely tied to Xenoblade or how distanced it is from Xenoblade, story-wise, "X" clearly shows that it's going to offer more of what made Xenoblade great -- namely rewarding exploration of massive, wholly unique landscapes with incredible fauna and some of the most amazing art direction I've witnessed in a game. But it seems that it's going to take all of that and expand on it exponentially. Couple all this with a great battle system, much more powerful hardware (which it seems to really showcase) and now, driveable mechs.
After playing Xenoblade and considering it one of the most expansive and ambitious games I've ever played, I then read that its director, Tetsuya Takahashi, viewed the game as "an experiment." "X" is intended to be the real deal. This blows my god-damned mind thinking about it.
For runners-up, Zelda for Wii U could get there, depending on what Nintendo shows us at E3; so could Retro's post-fucking-Donkey-Kong project, if it's Metroid or a new IP, dependent on the same factor. We got some big 'uns coming though -- I couldn't argue with anyone who said Metal Gear Solid 5, No Man's Sky, Bayonetta 2, Smash or The Last Guardian.
EDIT: Missed this question the first go-round:
Is it actually a sequel from Xenoblades or a brand new story line? Never played Xenoblades but am quite curious about this. Definitely looks great.
The very first reveal teased that the game might feature Xenoblade's protagonist, but that's all we know at this point. On the other hand, Xenoblade Chronicles is only tangentially related to the director's preceding Xenosaga games -- they share similar themes, and that's about it, as far as I've read. Though I wanted to, I never got a chance to play Xenosaga and I wasn't missing a thing when I played Xenoblade.
So it could go either way. We'll know after E3, I reckon.