Create custom maps
The popular remake of Rise of the Triad is adding support for quicksaving, as well as releasing mod tools in patch 1.2. The Ludicrous Development Kit will let crafty people make their own multiplayer or single-player maps, which other players will be able to download and use. You can also play without logging into your account now, meaning you can choose to not have your stats tracked.
I love crazy maps that people make for multiplayer games, and the addition of mod tools is making me think of picking this game up.