Zelda A Link Between Worlds

Within the last 5 years:

#1.) Nier
#2.) Demon Souls
#3.) Xenoblade

I was blown away by each of these games, especially Nier.

Bioshock.

Shin Megami Tensei: Devil Survivor Overclocked

Fallout 2, I didn't expect to like a RPG with those settings so much.
Same for Myth (edit: but not for the settings, I just didn't expect to like a RTS, although Myth games can more correctly be defined as "real-time tactics", not "real-time strategy")
Gothic, never heard of it when I got it cover mounted on a gaming magazine.
Thief series and the first Deus Ex: I expected to like them, but they even exceeded my expectations (even Thief III, despite its flaws).

Original Metroid on Virtual Console

Loved that one. I was already excited because it looked like a spiritual successor to A Link to the Past, but it was even better than I was expecting.

Muramasa Rebirth -- Playstation Plus game. No interest in this genre at all but I really enjoyed it and ended up buying Dragon's Crown by the same developer.
Rome Total War -- Big strategy fan and a friend of mine with bad video game tastes was telling me to borrow this game lol. I was like "uhhh okay" and then I played it and its become one of my favourite games ever.
Just Cause 2 -- Playstation Plus game again. Actually delayed downloading it for a long time as I had no interest in it. The concept sounded really lame but eventually I downloaded it and loved it. Looking forward to a sequel that can improve the story, weapon variety and add stealth.
Dragon Quest VIII -- Bought this game largely because it came with a demo of Final Fantasy XII. Maybe it doesn't qualify because Dragon Quest is an esteemed franchise and I knew it when I bought it, but I never excepted to like it as much as I did. It ended up becoming my 5th favourite game ever.

Agree on GoW 3 being the best hack/slash game ever, though I must admit my experience with the genre remains limited.

The Sacred Stones is still the only Fire Emblem game I played. Been trying to get the other one on GBA, but it can be expensive if you want one that's stood the test of time. I'm definitely interested in Awakening. In fact I should have bought it a long time ago already because it looks amazing (and the demo was cool), but you can be sure that it will be part of my collection at one point .

True about Fusion, it's just a different game. I completed both, and both styles are excellent I think. I used to think Fusion would be the black sheep of the Metroid family so I never played it until it came to 3DS. The spoon feeding didn't bother me much to be honest, because they did it well and tied to a good story. I should have realized back when it came out originally that it would likely be a good game though instead if dismissing it, because if anything, Link's Awakening also proved that a certain game's 'little brother' can be even better than the 'big console game'.

Furthermore, I think I can add a fourth game to the list. Can't believe I forgot about it.

Star Wars: Knights of the Old Republic: Even though I always liked the Star Wars franchise, the games were hit and miss for me. It has a lot of good games, games that ended up some of my favorites of all time, but also had a lot of mediocre ones or worse. I tried KotOR when my mother recommended it after playing the first part. I went in knowing little about the game. I was blown away. The game is basically perfect for my preferences. Gameplay-mechanics that seem tailor made for my liking along with maybe the most epic story to ever grace the field of gaming, amazing setpieces and levels and of course a classic soundtrack.

Same here buddy :) Its great to have a game to come out of left field and just blow all your expecations. Demon Souls was easily that for me :)

Another game would be Assassin's Creed 2 for me. I would also add Lost Odyssey. I didn't expect that the 360 would have one of my favorite JRPGs.