1.- Planescape Torment
2.- Dragon Age Origins
3.- System Shock 2
4.- Icewind Dale
5.- Morrowind
6.- KOTOR 2
7.- Mass Effect
8.- Baldur's Gate
9.- Deus Ex
10.- Chrono Trigger

And a special mention for Fable TLC, Neverwinter Nights, Fallout, Vampire Bloodlines, Pillars of Eternity.
Lastly, maybe I will be the only one who mentions this games but Pokémon Red and Blue deserve a special spot too.

1. Gothic II
2. Gothic
3. The Elder Scrolls III: Morrowind
4. Secret of Mana (SNES)
5. Deus Ex
6. Planescape: Torment
7. Star Wars: Knights of the Old Republic
8. Fallout
9. Fallout 2
10. The Elder Scrolls IV: Oblivion

Yeah, I wouldn't tip your hat about liking New Kids on the Block either.

Here's mine then;

1. Deus Ex
2. Vampire Bloodlines
3. Final Fantasy 11
4. Morrowind
5. Mass Effect
6. Shin Megami Tensei 3: Nocturne
7. Knights of the Old Republic
8. Vagrant Story
9. Dragon Quest 8
10. Fable

*Updated list to include Deus Ex.

1 - Age of Decadence
2 - Deus Ex
3 - Fallout
4 - Gothic
5 - Gothic II
6 - Serpent in the Staglands
7 - Star Wars - Knights of the Old Republic 2
8 - The Elder Scrolls - Morrowind
9 - UnderRail
10 - Vampire The Masquerade - Bloodlines

First on your list gets 10 points, last one one point. So it matters in which order you place the games! :-)

1. Chaos Strikes Back
2. Ultima Underworld
3. Baldur's Gate 2
4. Dark Queen of Krynn
5. Might and Magic 2
6. Icewind Dale
7. Dark Heart of Uukrul
8. Betrayal at Krondor
9. Wizardry 6
10. Morrowind

1. The witcher 1
2. Deus EX 1
(or 1. Deus EX 1
2. The Witcher 1)

you can finish my list as you want (but only with real RPG, no hack & slash (diablo like games), or TES games)

If you could choose games, not on gog, I would choose FF7 and Dragon Age Origins (3 and 4, or 3 and 4).

Ooh, you're giving points?
I will re-arrange my list a little :)

1. Final Fantasy X
2. Diablo II
3. Valkyria Chronicles
4. Ogre Battle: March of the Black Queen
5. Bastion
6. Fallout 3
7. Final Fantasy IV
8. Deus Ex: Human Revolution
9. Fallout 2
10: Titan Quest

Planescape Torment
ToEE
Arcanum
Fallout 1 and 2
Kotor2
Wasteland
Wizardry 7
Betrayal at krondor
Darklands
Ultima Underworld - stygian abyss


Honorable mentions:
Baldurs Gate
NWN
Icewind Dale
Might and Magic

1. Fallout 2
2. Fallout 1
3. Wasteland 2
4. Morrowind
5. Witcher 2
6. Witcher 1
7. Neverwinter Nights 2
8. Avernum Saga
9. Skyrim
10. Serpent in the Staglands

What do you know, all of my favourites can be found on GOG.

1. Wizardy 8
2. Anachronox
3. Geneforge
4. System Shock 2
5. Deus Ex
6. Might and Magic VI
7. Knights of the Old Republic
8. Gothic
9. Starflight 2
10. Avernum

I used GOG's definition of RPG.

1. Wizardry 8 - by a mile (or two...)
2. Jagged Alliance 2
3. Vampire Bloodlines
4. Deus Ex
5. Wizardry 7
6. Fallout 2
7. Gothic 2
8. Planescape: Torment
9. DCSS
10. Wasteland