This mod features "first-person strategy" with a real resource model and consequences for actions. Both sides are genuinely different and together they accommodate different play styles.
With Marines, fighting skill is less important, strategy and communication take its place. Playing as a marine will be a tense experience with methodical planning and strategy, interrupted with action.
On the other hand, playing as an alien will be an intense action experience, rewarding reflexes and alien heroics. Communication and coordination don't require typing.