I haven't seen this thread in about 2 months! 

though, being vodked i'm in the mood to compile:

quake
mdk
quake2
age of mythology
unreal
unreal tournament
carmageddon
tomb raider
blood
heretic 2

woot, it's 10 already, gotta stop. 

Not necessarily in order:

1) Age of Empires II.
2) ElderScrolls III: Morrowind.
3) Quake.
4) System Shock 2.
5) Deus Ex.
6) Half-Life.
7) Counter-Strike: Source.
8) Far Cry.
9) Thief II.
10) Beyond Good & Evil. 

Age of Wonders: Shadow Magic - PC
Car Wars - Tabletop
Homeworld: Cataclysm - PC
Money-Puzzle Exchanger - Arcade
Neverwinter Nights (SoU & HoTU) - PC
Pac-Man - Arcade
Quake - PC
Quake III Arena - PC
Samurai Showdown IV - Arcade
Wizardry - PC 

Mafia
IGI 2
Morrowind
Betrayal At Krondor
Hitman 1
Hitman 3
Quake
Fallout 1
Fallout 2

That's 9, uhh... 

i'm viney, so it should be ok, as well:

1. quake
2. gothic
3. gothic 2
4. ultima 8
5. doom
6. archon (c64)
7. giana sisters (c64)
8. system shock
9. newer game of your choice, let's say far cry
10. mortal kombat 2 (amiga)

the order may suck here and there, but deciding on favorites never really works out for me, anyway... all the shades of grey and blah... 

i already regret having posted that, for there are far too many games worth mentioning, all of the classic lucasarts adventures for example... 

It's implied that official expansion packs are included with the parent game. I am basing this on Single Player.

Quake
DooM
Unreal
Quake 2
Half-Life
Deus-Ex
Blood
Duke 3D
System Shock 2
Diablo 2


Honourable Mentions:

Wheel of Time
Undying
Return to Castle Wolfenstein 

Since I forgot a 10th item to my list, thanks for reminding me:

Blood :D 

-civilization 1
-quake (roughly qwtf, qwdm, sp)
Then after some gap
-star control 2
-indiana jones and the fate of atlantis
-the curse of monkey island
-ultima v
gap
-stunts
-slicks 'n' slide (1.28 or 1.29)
-s.c.out
-commander keen 4
-space quest 4
-wing commander 1

I've prolly forgotten some. I notice all these are from 1990-1996. That's when I played computer the most. 

-ufo
-red alert

Basically exposure to games has been a function of computer up-to-dateness as you can see. :) 

...and PC only, otherwise it would take forever.

Quake 3
Morrowind
Deus Ex
Trackmania Sunrise
Halflife 2
Quake 2
System Shock 2
The Longest Journey
Quake 4

Number 10 on the list would probably be Wolfenstein, or perhaps Vampire, or maybe Riddick...