I've decided to rebuild this post from scratch. This time I'll put the games in order and write a short explanation for every game. Or at least try to.
Edited the list a bit, Fahrenheit gave room for Planescape: Torment.
1. Arcanum: Of Steamworks And Magick Obscura
Yeah, that's right. I'm putting Arcanum on top. Sure, it's buggy. Sure, the combat system sucks major ass. However, even with all its flaws, the game brings probably the best role-playing experience ever to be delivered in form of a computer game. The options, even when set within the boundaries of the game, are practically limitless. Whether you play as a dwarven technologist or an elven mage, the game experience drastically changes depending on the player character.
2. Fallout
Even though Fallout 2 was the first game I played, I got to like the first game in the series much better. Sure, there are less locations, less NPCs, less items, less playtime etc. than in Fallout 2. However, the game has a much better atmosphere and feels much more complete than its successor, and that's what makes it more valuable from my point of view.
3. Planescape: Torment
Just doing my first playthrough, and I'm already hooked. This game probably has the most twisted atmosphere and plotline I've seen so far. In addition, the amount of written text is simply amazing, it made me feel as if I was reading a book at many occasions. The only downside is combat, which can be horribly confusing at times, but that would be the only objection I'd have for this brilliant game.
4. Fallout 2
There's not much to be said about this game, actually. As the successor to one of the the greatest RPGs of all time, it brought a bigger game world, more weapons and improved playability, among other things. However, expanding the game so much had its price. The unpatched game is ridden with lots of frustrating bugs and it doesn't feel as nearly as complete as Fallout. Even so, quite a lot of gamers consider it to be the best game ever made. Well, I don't.
5. Deus Ex
Deus Ex is often stated as a prime example of RPG/FPS hybrids. It offered a great story, lots of plot twists, great cyberpunk atmosphere, various locations and different ways of accomplishing objectives. You can storm in guns blazing, pick enemies off from a distance, sneak by the cameras and guards or hack through the security systems - the choice is yours.
6. Sam & Max Hit the Road
A point&click classic. The cartoony feeling and the humour make this game one of my favourites. Even though I've played it through numerous times, it still makes me laugh like hell, especially Max' comments.
"Gratuitous acts of senseless violence are MY forte!" *plink* *THUD* "You're such an adorable little imp, Max."
7. System Shock 2
Another RPG/FPS hybrid. Awesome story, different approaches, great character development and, in particular, a brilliant atmosphere. Even though it's eight years old, I still haven't encoutered a game that would have kept me on the edge of a knife so much. Well, one game has come pretty close, and it's at the end of this list.
8. StarCraft
A classic. The game offered three completely different races to choose from, great gameplay and a good story to keep it together. The best aspect of this game, though, is the multiplayer. It offers counless hours of fun over the Internet and LAN with custom maps and loads of different tactics used to outsmart your opponent.
9. Full Throttle
Another LucasArts' masterpiece. A great mix of humour, adventure and action, packed up in an extremely stylish game. Great puzzles, a badass main character and a conspiracy plot. What more can you ask for?
10. S.T.A.L.K.E.R.: Shadow of Chernobyl
At the first glance, this game looks like another generic FPS. However, it's the RPG elements that lift this game above average and set it on my list. Also, the atmosphere is just awesome. Everything, from large open areas to small, claustrophobic ex-Soviet military installations provides an excellent post-apocalyptic atmosphere. This game has managed to scare me nearly as much as System Shock 2 did. Unfortunately, there are quite a lot of bugs and balance issues, but, as DDD once stated, bugs can be fixed but shitty design is forever.