For me, it's probably Wasteland 2. Although strictly not a 2016 game, the 'final' release of it with the revised graphics engine was started by me, this year.
It remained true to the original format of WL1. Added dialogue to characters that you actually cared for and had a story that was involving. I really like games where virtually impossible odds at one point, can be returned to for a much fairer fight later on. The fact that you had some serious ethical decisions to make during the game, also added to its impact for me. The fact that I've pumped over $100 into the preorder for WL3, must speak for something, too!
A very close 2nd place has been DiRT Rally. My racing game of choice at the minute.
As for disappointment (well, let-down is probably more apt) - I'd have to say DOOM. It's been a long time since I've had a game installed that I just wish would hurry-the-f*ck-up and get completed, or get deleted - it is consuming 80GB+ of valuable SSD space. For a quick arcade mode blast - it's enjoyable. The campaign however, is an example of great ideas, but poor execution. The weedy weapons. The ammo usage on par with ten firing miniguns at once. The over-reliance of special firing modes. The trigger-points for enemies usually happening in a cut-off map the size of a backyard. The list goes on. It's a frustrating if good-looking game to play and comes with perhaps THE most useless map I can recall in an FPS. Shockingly bad - even when it's 100% revealed. Carnage and bedlam are well represented in the Serious Sam games and Warframe to a certain extent. DOOM doesn't have this. DOOM just makes you want to run & hide... when yet again you emptied all the guns at your disposal.
People who play DOOM on the hardest difficulty are the gaming equivalent of the freaks who have their tackle stamped and mashed down upon by a woman in high heels. It isn't fun. It isn't pleasurable. It's just tortious, lingering and repetitive agony.