Original War. A very unique RTS about American and Russians fighting over a precious resource billions years in the past. It has an interesting story with memorable characters and branching choices. The game still looks decent, especially the between missions cutscenes didn’t age badly because of the style of presentation. One thing that’s rather hit or miss is voice acting, at least in English. There are two campaigns so you get to see both sides, skirmish mode, map editor and quite a number of mods. Some interesting mechanics like vehicle and building customisation. You can build not only combat vehicles with various weapon systems but also utility vehicles like trucks to haul resources and cranes to help with construction. You can pick propulsion method, tracks/wheels, size and if it’s manned or unmanned, and each choice has some upsides and downsides.

The thing that stands out the most is that it’s the only rts I can think of where you actually care for the life of your soliders. Due to the setting, there’s no way to recruit new people, so losing anyone hurts, and you will be grateful for unmanned vehicles, trained primates and others methods that reduce the risk to your soldiers.