Never able to play the original, because it wasn't on PC, but I do think a decent adaptation could be done.
More so for the 'Terminator' series, in all honesty. Perhaps from a Skynet-only perspective, because that would be the most fun and the human units wouldn't be as interesting or diverse, unless it began with them gaining control of some Skynet factories: But then, why wouldn't Skynet just destroy them? Plus, Terminator versus Terminator would be confusing.
Aliens, Predators and Marines would be different: Only the Marines could have much in the way of diversity. Predators and, especially, Aliens are best portrayed as one-size-fits-all. At the most, you could have 'light' Predators and 'heavy' Predators, but that would be just about all there should be or it gets silly.
Alien unit diversity would run a huge risk of not only being silly, but infringing on copyright of Tyranids, from the 'Warhammer' series. Maybe capturing different wildlife for different body designs? But they should all be just about as strong as one another and it's not like they'd have different abilities.