Master of Magic
Descent
Freespace
Panzer General 2
IL-2 Sturmovik
Pirates!
Tyrian 2000
Wizardry 6
King of Dragon Pass

These are the titles I've enjoyed immensely since discovering them here.

I really should get MoM at some point, and XIII, and ..... awww

Edit: greatest game I discovered here, Sacrifice hands down.

Agree 100 percent. Hadn't heard of it, bought it immediately and even gave away a couple of extra copies on my website I loved it so much :)

The two games on GOG that have surprised me the most recently about just how GOOD they were are XIII (which unfortunately isn't on GOG any longer -- hope it comes back), and Cossacks, which I'm currently playing and having a blast with.

I was also blown away by Lands of Lore 1 (could definitely do without 2 and 3 though :), Clive Barker's Undying was one of the best games I've played this year, and I also loved Darkstone.

Biggest disappointments? Legend of Grimrock -- really really really wanted to like it, tried playing it three times, rage quit every time, and Fahrenheit, one of the worst games I've played -- ever.

Perimeter
MDK & MDK2
Theme Hospital
Evil Genius

I thought maybe I'd bump this if anybody else that hasn't posted wanted to.

Well I rediscovered Battlefield 1942 and its still an awesome game.

Duke Nukem 3D and Shadow Warrior

System Shock 2. I have never head of it before I came on GOG. It took me a while to actually get it but it's one of the best purchases I've made on GOG. :)

Sure! Some old, some new, in fact.

But for older games, I'd have to say

- Ground Control 2
- Lords of the Realm II
- Smugglers series because of Smugglers V
- The Last Express
- Chaos Overlords
- King of Dragon Pass

Fallout 2. Really, just freaking amazing in many ways. Not remotely perfect, but really just great. Others:
Worms 2, Arcanum, Divine Divinity (hardly old really, but, you get it.) and Rise of the Triad is magnificent.