Almost no other game has left a lasting impression, and certainly not a game that I got for free with a joystick. One of the very few RTS-FPS games to ever exist, it occupies a niche that almost everyone will miss that isn't a fan. Squad-based RTS vehicle combat gameplay combines a fascinating post-apocalyptic art-style, with extremely intense FPS vehicle combat against hordes of aggressive foes. You can (and must) fight in the middle of your own army, while trying to manage resources, scouting, building, reconnaissance, and defense; all while in combat. The uniqueness of each faction, the intensity of the story that comes with it, the destructible environments, and the wonderful mission text adds an environment that shows how much of a passion project it was. The devs even recorded themselves in the campaign win video.
Hamburger Hill is probably the greatest level of a game I've ever played, and without a doubt the most intense. For 10 minutes you must survive 3 v. 2 v. 1 over a power-station, and a Studson (atomic) bomb that will level everything on the map except whomever controls it. You must fight hordes of enemy units from all directions, some of them fighting each other, as you struggle to hold key points, as the time counts down. If you survive long enough, the bomb goes off, and you get to watch the shockwave destroy hundreds of enemy units and buildings, leaving you in a moment of quiet contemplation over your success with your remaining handful of vehicles that managed to make it through.
This is precisely the type of game that needs preserved. The gem that no one noticed despite the fact that it was in their face. The gem that time, the companies, and the media, but never the players, forgot.