Having read this topic some months ago, i downloaded and played Fallout 2. Though i'm not a fan of RPG-like games, that was really cool. So, thanks for the hint
i recommend civ2. spent eternity on it. fun as hell and you can probably get a free download.
A nice feature is that the rules are set in text files. You can change the rules of the game (Within limits)!
Yes that was fun! You could easily change graphics/sounds too (they're simple gif/wav files) and i used to create whole new units.