The PC's got a phenomenal, unparalled history as a gaming platform – a good two decades of wonder and weirdness.
The trouble is half it a) looks like ass on high-res displays b) plays like ass due to ancient interfaces c) flat-out won't work on our fancy modern operating systems. Crazy fans to the rescue!
Step forward Freesynd, an early but hugely promising attempt to recreate the original satirical, sadistic, dystopic squad game. It's only a couple of levels for now, but it does include almost all the sound effects of the original game, as well as the intro and nostalgia-inducing Bullfrog logos.
Thief: The Dark Mod
Half remake and half sequel, this aims to bring the values of the original two Thief stealth games into the e'erimpressive spooks 'n' shadows of the still robust Doom 3 engine. The team are very careful to avoid copyright infringement, so don't expect to see master tea-leaf Garrett namechecked as such, or any borrowed assets, but it's definitely Thief.
A whole new Thief game, which is probably more exciting than a mere remake. It's very early days for it, but a beta release is due soon (there's a small alpha one already available) and it's already impressively unrecognisable as being Doom 3-based. (Thief: The Dark Mod homepage)
Dune II
The firm-chinned granddaddy of real-time strategy has never been bested in terms of out and out thematic appeal (three intergalactic houses warring over spice, on a planet infested with giant worms and crazy nomads who drink their own wee. Come on!) but its interface has aged horribly. No group select, no hotkeys, no building rotation…
It's genuinely, tragically a chore to play now. In a strange piece of ironic resonance, three fan remakes are vying for the right to be its heir.
Choose from Dune Legacy, which uses some of the original game's art and sound assets, Dune II: The Sleeper Has Awakened, a ground-up attempt to incorporate modern RTS interface/UI values, and Dune II: The Maker, eight years in the making but still in demo stage.
FreeOrion
If you prefer your strategy a little more galactic, then you'll doubtless dig this free open-source space trading/colonisation and combat game 'inspired' (yeah, right) by the venerated Master of Orion series.
Its current v.03 release is deemed "essentially complete", but there are a ton of fixes, polishes and incidental features yet to come. Keep an eye on its progress at freeorion.org.
Freerails
Railroad management games are thin on the ground in these days of hi-def manshoots, but this java-based remake of Railroad Tycoon might just scratch that itch of yours. It's even got online multiplayer built-in. Give it a whirl.