Another recomendation would be Battlezone. Fighting in hover tanks on Venus definately qualifies as Sci-Fi.
It's one of the finest games ever made. An unique mix of Quake [or any FPS], Command and Conquer, World of Tanks and The Settlers. One of the best control schemes to manage your units I've ever seen. A top notch story and voice acting which emersese you into it.
It was remastered as Battlezone98 a couple of years ago and I think they forced down the freeware release which itself was patched to work on later windows by one of the original developers. Hunt it out, you won't be disappointed.