I feel like I need to post something about how much fun I just had. For what ever reason I never played Half Life, maybe my parents thought it was too brutal or something. I got my first computer in 96 and Red Alert 1 was my very first game. Anyways, I just played through Half Life vanilla and loved every second of it. I forced myself not to look at guides or walkthroughs and spent a few hours stuck and frustrated but the eureka moments were worth it. It seems that older games are the only ones that can deliver those kind of eureka moments, What else have I missed??? I have got got some free time over the holiday season please post some suggestions. I just wanted to share how awesome of a time I had.
System Shock
Deus Ex
Max Payne
Driver...
These are some really nice classics
You could pick up entire Half Life series, which is pretty good IMO. They're still old, but not that old.
Now you see where the frustrated "half life 3 confirmed" meme comes from :) It's been 8 years since the last game in the series came out.
Try Half Life 2 and the two "Episodes" after it, Portal is nice too... I also highly recommend MDK, one of my top favorites from the 90s.
If you haven't played both episodes of Half Life 2 I'd really recommend it. I some what preferred it over the first game in fact and it definitely keeps the same feel from the first game.
This is newer, but bioshock 1 and 2 are practically free and have a really cool story line.