Assuming MGS5 doesn't get released in 2015, probably The Witcher 3. I think it's a pretty safe bet to say MGS5 isn't going to be released in 2015.

Zelda...assuming it releases in 2015.

Splatoon if not.

I have a feeling punching at my gut telling me it will dissapoint. Dunno why, just do.

Generally when something looks awesome, it doesnt translate that well.
Also I didnt play ground zeros so I cant judge whether that was good or not.

From official announcement/release date, i would say XENOBLADE!!!!!!! ( X )

I think this game would somehow last me for a very long time =D Hard question though

Xenoblade Chronicles X

Think I'd get the most bang for my buck that way in terms of quantity (playtime) while still being VERY high quality. Plus, it's a spiritual successor to my fav game of all time. Also, since Zelda will release the Friday before Thanksgiving, it wouldn't be THAT bad to wait until January 1st to play it.

But, if I could only EVER buy one of them...at the moment I'd still say Xeno, but further updates, more information, and a proper trailer for Zelda could change that. 

ARRG. SO HARD.

I'm SORELY tempted to say Majora 3D, but I don't know if any remake is worth giving up ALL the other games for a year. I gotta say Bloodborne because we KNOW it'll at least be good.

Zelda U, even though currently, Uncharted 4 is my most anticipated game for next year.

Zelda

Xenoblade Chronicles X. Just too much of a fanboy and I know that game would last. Zelda is also big but I have plenty of Zelda games to catch up on, and while there are lots of other great series, if I had no choice, I'd rather suffer through not having them than not having XCX, lol.

Uncharted 4, hands down.