Arcanum
Anachronox
Sacred Gold
Giants: Citizen Kabuto
Planescape: Torment

In alphabetical order:

Fallout 2
Gabriel Knight: Sins of the Fathers
Planescape: Torment
Sanitarium
The Cat Lady

Honorable mentions: Teenagent and Jack Orlando (those were the big things in Poland back in the old days and I knew both by heart), Earthworm Jim 1 and 2 (those memories!), Blackwell series (redheads!)

VERY difficult to pick my top 5, but so far I'd choose these, in this order.
1. Shadow Warrior
2. Little Big Adventure
3. Realms of Chaos
4. Treasure Adventure Game
5. Alien Shooter 2: Reloaded

Fallout 1+2
Crusader 1+2
Jagged Alliance

Sid Meier's Alpha Centauri
Ultima VII
System Shock 2

Those alone merit placement.

1. System Shock 2
2. Beneath a Steel Sky*
3. Oddworld: Abe's Exoddus*
4. Fallout
5. Tyrian 2000

*played, but not via GOG.

Note: subject to change; this may be completely different next time this thread is bumped.

1. Planescape: Torment
2. Fallout 2
3. The Longest Journey
4. Thief
5. System Shock 2

Thanks. Yeah I probably bump the Humongous Entertainment thread more than I should, but I'm very surprised a thread like this isn't more popular as everyone can get involved!

1) Uplink
and in no particular order
- Pharaoh + Cleopatra
- Zeus + Poseidon
- Divinity II - Developer's Cut
- and... nope. No 5th game yet.

Psychonauts
Settlers II, 10'th ann.
Beyond Good and Evil
Sid Meier's Alpha Centauri
Driftmoon

edit - hey, I did this before. My list have changed a little :)

My list would be quite a bit different now after two years. XD
I'll have to think about that.

1) Fallout 2
2) Planet of Death*
3) Freespace
4) Blood
5) Worms 2*

* Own the original game cd.

Fallout
Tropico
The Witcher
Alpha Centauri
Panzer General II

Master of Orion II
Deus Ex
Heroes of Might and Magic V
Fallout
The Blackwell bundle

Special mention: space rangers 2 (but it has been pulled off).