And which ones are you planning on buying next?
I bought Kingpin and the three Fallout games. I've owned Fallout 1 and played Fallout 2 and Kingpin before, but never finished the latter two. I never played Fallout Tactics before, but I remember liking the combat system of Fallout 1/2 so I hope I'll like this game.
Other games I'm definately going to buy: Lionheart and Operation Flashpoint.
Games I'll maybe buy: Sacrifice, Giants, Jagged Alliance 2 and Soldiers.

I have bought Original War, Lionheart(with the free game code) & more recently Soldiers.
Most of those Interplay classics like Sacrifice, Giants, Evolva, MDK 2 & Descent 3 & etc I have already owned or had played b4.

I've purchased the Fallout set, 1, 2 & Tactics. I've never played any of them before.
Future purchases will incl. Freespace 1 & 2, as well as Op. Flashpoint (even if the good people @ PCGamer didn't like it so much).

Fallout, Giants, Redneck Rampage Collection.

So far just Fallout 1 + 2, which I hadn't played before.
Looking forward to Earthworm Jim 1 + 2 (I gave away my PC copy of EJ1 and still own my SNES copy of EJ2, but I'm just gonna buy them again) and Second Sight.
I might also pick up Earthworm Jim 3D and the MDK series.

Fallout 2 and Freespace 2
Basically as I am off work, on an old laptop that can't play anything well...
Once I get my desktop working again... I'll be mixing these games with a healthy mix of Bioshock and Crysis

I bought Hostile Waters and absolutely didn't regret it :) I used the "free game"-coupon for Fallout 1, which I have yet to play, but I am very interested in it. I already own Fallout 2, but even though it may get better later on, I just didn't have any fun in those first couple of hours, didn't want to go on and still don't feel like doing so. As I've heard Fallout 1 is all I want, anyway: Better beginning, easier to get into, more serious.
My next purchase is likely going to be Giants: Citizen Kabuto. I was never interested in it and never got any information on it, as I always thought it was a fun but mindless shooter. It's just now that I found out it also has strategy elements like building bases, which got me very excited about it :)
I was also interested in Original War, but the highly mixed reviews made me skeptical and the demo crashed twice without any notice, so I didn't get it.
Apart from that the games catalogue doesn't include anything I am very interested in, so I'll just wait what else is to come :)

Enough to realize this site will eat my credit card. :D
Descent 1+2
Descent 3
Freespace
Freespace 2
Redneck Rampage
Stonekeep
Shogo
MDK
Fallout Tactics
Down the line I'm also getting EWJ 1+2 and Second Sight.

None (out of currently available ones I have a few and I'm not interested in the others).
Yet I'm still waiting for a few titles to purchase...

I already own pretty much all of the games that I want to from GOG's current catalogue, but I bought Descent 1&2 and Freespace 2 again to show my support for the amazing idea.
...that, and I feel like playing them but can't be bothered to search through my currently boxed possessions to find the disks. (Currently moving house)

Fallout 1 and 2. Never played then before but been wanting to for years and could never find them in shops.
I'm thinking of buying MDK or maybe Freespace 2 but I can't decide if I should and if I do which. Arrrrgh decisions :P

- Redneck Rampage Collection
- Descent + Descent 2
- Descent 3 + Expansion
- Giants: Citizen Kabuto
- Messiah
- Kingpin: Life of Crime
Now I'm very interested in Toca, Colin 2005, Perimeter, Second Sight and probably I'll also buy Kingdom.

So far I've bought
-Descent 1 + 2
-Fallout 1
-Descent 3
I want to get, well, pretty much everything :).

I remember stonekeep vaguely, and from that I remember I didn't care for it.
I did pick up two games I basically missed that I heard at the time were good,
Die by the Sword and Freespace2

Only Freespace 2 at the moment.
Will buy Second sight when it is available.