Edit:
*Added Warcraft 3
7: Assassin's Creed 1&2
The latest game series I've been playing... completed #1 about three weeks ago, and I'm pressing on with the second. Great story, good gameplay... but sometimes a little repetitive and samey. Still fantastic though; looking forward to playing more of it.
6: The Lord of the Rings Online
LOTRO is my second-favourite MMO I've played. It emphasises questing and levelling more than WoW, which are some of my favourite MMO aspects. It loses marks for being VERY on-off. Sometimes the game is phenomenal (mainly when directly dealing with The Fellowship) and at others its just plain boring (i.e. questing in the barren zone of Angmar). However, the player-base seems more mature than WoW's, despite the fact that it has gone F2P.
5: Elder Scrolls V: Skyrim
Can't say enough about this game, it's by far the best game of 2011. All the memes have made the game lose its touch a bit, but apart from that it's phenomenal.
4: Warcraft 3
The single-player mode of this game is absolutley fantastic! Story 10/10, Gameplay 10/10. Loses marks for having a less interesting expansion, and rather boring multiplayer.
3: World of Warcraft
The game we all know and love. I have huge love for this game, even though my love for it has... lapsed... in the past few months. I've got the Annual Pass, and I'm looking forward to MoP, but 4.2 and 4.3 haven't impressed me massively. When I look back at 3.3, I feel a little sad for how much fun I had... but maybe that's just nostalgia. I really want MoP to be great... don't screw this up, Blizz.
2: Monkey Island 1,2 & 5
I played MI 1+2 for the first time last year on my iPod touch. I played every day on the bus two and from school, and I got addicted. The games are hilarious and have brilliant stories. The latest edition (Tales) is also a fantastic addition to the story, even all these years later. I've not played the 4th Monkey Island (as its not rated amazingly), and the third I had but didn't get into it as much (the change of style is a bit weird). This game loses a few marks for having an odd MI2 ending (as Gilbert left the studio after MI2, the ending was not resolved).
1: Simon the Sorcerer
A perfect Monkey Island-esque duo of adventure game (there were two good ones, the rest were 3D and look awful). I mainly love this game due to the fact that it's one of the first fantasy games I ever played... it's a bit "generic fantasy" but it's got great graphics, a funny story and fantasting puzzle-play. A perfect game... loses marks for the iPhone version being so buggy that I fear people will not appreciate the game's genius.