Fallout 2
Civ IV
Arcanum
Deus Ex
VTMB

That's pretty much it. My own personal golden age of gaming is encapsulated by those games, 1998-2005.

Every from my early games.
Later mmmh, Pirates!, Fallout, Monkey Island, Pool of Radiance, Final Fantasy, Zelda, Castle Wolfenstein, Doom, Quake.

From GOG.com:
- Tales of Monkey Island
- Back to the Future: The Game
- Fallout
- Beneath a Steel Sky

From elsewhere:
- Metroid Prime
- Metroid: Fusion
- Doom
- Putt-Putt Goes to the Moon

I second both Arcanum and Fallout 2. Both Witcher games for me, although in the second one I almost got bored with Flotsam because it was not very easy to run and just in general is the least enjoyable part (don't know if this is a spoiler, but things get really good in the next chapter and the next starts out fine, but ends far, far too quickly. I debate whether too long or too short is preferable.) Non GOG, but Fire Emblems: Sacred Stones, Path of Radiance, and (same boat as Witcher 2) Radiant Dawn. Generally Zelda and Metroid games do this (for Metroid Zero Mission and Prime 3) and EDF: 2017. Oh, and any Soul Calibur game, those are really good. Unfortunately, I will get either bored or out of the mood for some games I think are really good and leave them let sit for long whiles. Oh, Medieval II: Total War is a game which I always go back to, sooner or later.
Might just have to get that sometime...


Edit: While I'm on the subject, the space ship shooter mini game from Spy Fox was really good.

I downloaded the ScummVM file and sat here for the
last two hours and played like a happy six year old! :-)
Silly fun.

Thanks for all the answers everyone. Lots of good ones, so I'm gonna cop out and just pick the 1st one as the "answer." Thanks!

The best game on GOG is Betrayal at Krondor. No game ever made has done everything right - the story is great, the characters are greatm the exploration is great, the RPG system is great, the combat system is great, there's literally nothing about the game that is bad.

I was absolutely mesmerized when the original Quake arrived! It was amazing to see the technological leap from Doom's 2D sprites to Quake's full animated 3d polygons!