Been surprised by a few games over the years for both good and bad reasons. More recent ones that stand out (for positive reasons) are:
Dying Light: Agreed on this one. Loved the mechanics in this game, just felt so smooth and satisfying to play. Story was also pretty decent up until the expansion introduced daft spiritual/cult elements to the story.
Mark Of The Ninja: Genuinely brilliant 2D game with stealth mechanics that could teach some AAA games a thing or two. loved the way you felt more like the hunter than the hunted and could use your intelligence as well as your tools to creatively clear a room however you wanted. Played it through a few times and did virtually everything slightly different each time.
Doom 2016: The most recent on the list but this was a franchise I was never a huge fan of so I was amazed when I pretty much fell instantly for this game. One of the most smooth and fluid gaming experiences of recent years. Looks gorgeous, runs like a dream, and fast frenetic fun throughout. I even liked the bosses.
Portal 2: I'd guess most people would pick the original and I can see why but this was actually the first of the two I played and as much as I love the first game this one is just something special. Ellen McLain as GLaDOS and Stephen Merchant as Wheatley were both phenomenal and had me chuckling throughout. Added to the already brilliant game mechanics it was a winning formula and created one of my all time favourite games.
Dust: An Elysian Tail: Bought in a sale as a bit of a time killer it shocked me how much I actually ended up enjoying this game. Sure it was hardly original but it had an addictive quality and I was hooked almost from the start.
Life Is Strange: I honestly thought I would hate this game. Set around two students and on a University Campus....seemed like it would be everything I hate but I was absolutely gripped through the entire story. I even grew to care deeply for the characters who were voiced to perfection. One of the biggest surprises of my entire gaming life and one I'd put alongside any of the Telltale games.
Ori & The Blind Forest: Finally this one I thought would also be a good way to kill a few hours whilst I wasn't playing anything else. Cute platformer I thought...only this was far more. Everything from the hand painted look of the game to the gorgeous soundtrack was pretty much perfect. I also loved the Metroid element to the platforming and though the escape sections were a little frustrating they didn't in any way ruin the experience. Beautiful game!
Probably one or two more but my brain is a little fried today so nothing else really comes to mind.