Cybernator is fricken awesome, and definitely the best game of its kind.
Target Earth is okay too - I recall people complaining straight away how difficult it was, but I did beat the thing, so I must've been one bad mofo back in the dayz (never played it again).
AS Valken 2 is good stuff too, but yeah, it just isn't as slick as Cybernator/Leynos, and I agree that it hasn't aged as well.
Blood Gear is also awesome, definitely one the gems of PCE, but not quite Cybernator good.
Ranger X... I never understood. I really did try liking this game (considering I I liked ALL the games mentioned above) but I just never saw the appeal. After about 2 levels, I just get bored & turn it off.