Alien: Isolation looks phenomenal.
I didn't play a lot of games released this year, but here's the cream of the crop. All together, it was a fairly good year for gaming, with quality trumping quantity, and there were plenty of interesting releases that I haven't played yet (Far Cry 4, Wasteland 2, Dragon Age, Divinity, etc...) but there are always Steam sales to add to the collection, and I wanted to make sure my backlog didn't get too outrageous. Only buy something you plan on playing, unless you like wasting money.
Best RPG: Dark Souls 2--Probably my favorite game of the year, if I had to pick one. It looks better than the original, plays better than the original, is less frustrating than the original, yet it lacks a certain quality that Dark Souls had in spades. I think it comes down to world design--the original game had a vast, open world which the player was free to explore at will. Dark Souls 2's levels feel like separate arenas, cut off from each other, though they do have more variety than one might expect. Similarly, the vague story is less arresting than the tale of fallen gods in Dark Souls. Despite these minor complaints, I spent 90 hours in this game. Recommended to those who like deep action RPG and considerable challenge, though its difficulty is exaggerated (except for optional bosses: the gargoyles, ancient dragon, and the darklurker are harder than anything in the original game). Probably best to wait for the extended edition which adds new areas and includes graphical updates and DLC to come out later this year.
Best Stealth/Horror/Survival Game: Alien: Isolation--Somehow, Creative Assembly made a game that accurately reflects the feel and themes of the original Alien film. This is a sneaker, not a shooter; you can't kill the alien, only hide from it and drive it away. Marooned on a decommissioned space station, every level has perfectly captured the retro-futuristic look of Alien. The environments look lived in and feel grimy and working-class. Think of the game as a non-RPG heir to System Shock 2. Recommended to those who aren't scared of video games and enjoy hiding in closets and air shafts.
Honorable mentions: The Banner Saga, Thief--I haven't play much of the Banner Saga, but I dig its graphics, which resemble a 70's animated film, as well as its turn-based combat. It might be a little heavy on fantasy politics, however. I also enjoyed the Thief reboot, to a certain degree. It wasted a lot of the excellent universe that the original series created, as well as crammed unnecessary button mashing sequences and boss fights into a Thief game (why, oh why?). It did, however, have a solid stealth system, and it looked pretty good. A wasted opportunity. Buy if on sale.