I would say games that rely more on gameplay mechanics than on presentation age better than the other way around.
Tetris is probably the perfect example for a "timeless" game.
And I wouldn't count Railroad Tycoon among the "badly aged" games. Once you can look past the clunky graphics the game still has a lot of charm.
For me games that didn't age well would be ie. the old flight sims like F-117A Nighthawk. While I loved them to death back in the day, those games (for me!) have always been about immersion, and I'm having a hard time recreating that feeling with crude HUD, clunky cockpit and pyramid hills nowadays. IL-2 Sturmovik is about the lowest I can handle in this genre. But I can see that other people might see this different and can still enjoy the cat-and-mouse with the radar, looking past the featureless landscape and the blocky HUD.
sunshinecorp: Mass Effect AGED? HOW OLD AM I? HOW. OLD. AM. I.
NOOOOOOOOOOOOOOOoooooooooooooooooooooooo.
If Mass Effect is old... *damn*