It really is. Seeing as Starbreeze are developing Dark Athena, I'm hoping for even more improvements. I hope Vin Diesel's input into the game is at the same level as before, as the RPG element came through really strong.

Read a review of that a long time back and always wanted to play it... thats the kind of game i'd like to see on GOG... something unknown or underappreciated that i can try out at a budget price.
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1 - Terminator: Future Shock (+skynet)
Awesome FPS with great atmosphere and weapons. First real 3d FPS with mouselook i played. Realistic Environments. Driveable and flyable vehicles. Ahead of its time. got eclipsed by quake a month or so later.
2 - Chrono Trigger
With its DS re-release its finally getting noticed. But for years the Final Fantasy games got all the hype, and Chrono Trigger blows them all away.
3 - Jedi Knight (DF2)
Another totally awesome FPS. great story and atmosphere. Great gameplay and weapons. Great Enemies, level design, environmental puzzles, story. Great RPG elements and light/dark story. Got eclipsed by Quake2 and seems to have a suprising lack of online reviews and gamerankings presence.
4 - Space Hulk: Blood Angels
OK, it had lots of flaws. (controls, bugs) but it had an awesome mix of FPS and tactical overview gameplay. It could get darn scary at times, with genestealers coming at you from all angles and your teammates shouting warnings at you. The command time mechanic was great for single player... can't believe every SP rts didn't copy it.
5 - Call of Cthulhu: Dark Corners of the Earth
Great FPS/Adventure with loads of atmosphere. First half is much better than the second.. and the last level was unfinishable on the PC for me, without cheat codes. But it was cool enough that i'll overlook the rough edges. If it had had AAA polish it'd have been one of the best games ever.
6 - Eternal Darkness
Awesome Resident Evil style game, got mostly overlooked due to being an early gamecube title.
7 - Kohan
Good RTS that most people have never heard of. Not great graphics, but tactical squad combat rather than rushes and base building.
8 - Hostile Waters
Played for the first time here on GOG. Never heard of it before. Great mix of RTS and action game.
9 - Hidden & Dangerous
Maybe the game that started all the Realistic WW2 games that have followed. Bugged to hell, but great game underneath.
10 - Scorched Earth
Everyone played this at school... the game that started the worms style genre.
10a F-zero 64
Awesome racing game with great tracks.. personally I preferred it to mario kart 64.
I'm sure there are others, but i can't think of them off the top of my head.
These aren't (all) the best games ever... but they were underrated.
Thief, System Shock 2, Deus Ex, Psychonauts, Grim Fandango, Beyond Good & Evil weren't all commercially huge, but i think they are pretty universally regarded as great. etc..