Did my duty as a SteamGAF member and voted. Huzzah. Here are my thoughts, which you can read or ignore at your leisure.
Honourable Mentions: Divinity: Original Sin, Metal Gear Rising: Revengeance, Endless Legend, The Banner Saga
5: Wargame: Red Dragon - The RTS Genre hasn't had the best few years recently, but the Wargame series has stood out to me as an excellent example of the genre. Once you get your head round the complexities of the game, you've got a great RTT/RTS game with cold war era forces battling it out on land, sea and air.
4: Valkyria Chronicles - A shining example of how to port a game to PC, this was an unexpected but very welcome addition to my PC library this year, and excelled in many ways. Stunningly beautiful thanks to it's unique artstyle, I really enjoyed the turn-based/realtime combat.
3: Dark Souls II - Another excellent example of a PC port. There's real greatness in the Dark Souls gameplay, and that feeling of learning from your mistakes against an enemy to triumph over them is really something special. The DLC though really pushed this game into my top five, with fantastic level design and boss fights.
2: Shadowrun: Dragonfall: Director's Cut - Durante has rightly spoken about how this year saw a CRPG renaissance, and I feel that Dragonfall is the shining example of that renaissance. Sure, Divinity's got the best combat out there, but Dragonfall has a fantastic story and wonderful characters that you really want to get to know. I could just spend ages walking around the Kreuzbasar talking to everyone, before heading off on another run.
1: Transistor - Transistor is divine. It's an amazing mix of a near perfect soundtrack, jaw droppingly gorgeous visuals and challenging, flexible and rewarding gameplay that comes together to create something truly magical. It's one of video gaming's few tragedies, full of moments that'll stick with me for a long time, from the first scene right up until the bittersweet ending. Transistor is easily my game of the year.