I remembered one other cool freeware game Street Rod that would make a good addition here, especially given the general lack of old racing games on GOG.

Sherlock holmes and the Mystery of the Mummy. The first spin-o-rama adventure from frogwares is free in steam from a long time. it use to have problems in fullscreen in modern computers, so GOG could be the ideal place to live.

Not sure, if it´s still free, but Gog should get Full Pipe.

Warning: Trailer contains spoilers.

Planet's Edge.

I'd say The Lost Vikings. I'd even pay for it if GOG worked its magic and made it run out-of-the-box.

Marathon series for me as well.

Also, Abuse is a game I think should be here.

Gravity Bone
http://www.blendogames.com/older.htm

It's just that getting some old games to work can take a lot of tweaking and headaches. For example, last time I tried to install Colonization through DOSBox on my own (long before learning of GOG) I needed one hour just to make sound work. I like how GOG takes care of that. ;)

Ken's Labyrinth

Supaplex (1991)

Wishlist
Gameplay

Clyde's Revenge (1995)

Wishlist
Gameplay
Download Page

Skyroads (1993)

Wishlist
Gameplay
Download Page

Oh, definitely.

I tried that one recently, but my quick impression was that the keys were all over the place. Did you remap them somehow?

I don't think you can remap the keys. But once you get used to them they're pretty comfortable:

Arrow Keys:
Movement (Go Left/Right, Climb Up/Down)

‏ Ins / Ctrl:
Switch to Other Players

‏ F / SPACEBAR:
1. Erik Jumps
2. Baleog Strikes with Sword
3. Olaf Holds Shield Regularly or Over-Head (Hand-Glider)

‏ D:
1. Erik Bashes things with Helmet (while Running)
2. Baleog Shoots Arrows
3. Olaf Holds Shield Regularly or Over-Head (Hand-Glider)

‏ S:
Push Buttons / Flip Switches / Talk / Activate Teleporter /
Activate Various Machines / Get Hints Near ? Icon

‏ E:
Use a Selected Inventory Item

‏ Tab:
Select an Inventory Item

‏ Tab.. Then F:
Select an Item and Give it to another Viking