Cue the screaming Saturday matinee children.
How did the embryos survive all of these years? Don't know. Don't care. How did these eggs get on the moon and why did we find no evidence of adult specimens? Don't know. Don't care. Why do all aliens look like lizards? Stop. Just stop.
Seriously, Bryan Dunn did a good job with this one. First off, it is well written in a B-movie style. Secondly, confining the action to a small area (mostly an abandoned cave and mine) and focusing more on suspense than relentless bloodshed helped ratchet up the tension and kept the story well contained and enjoyable. Consider this an homage to those great creature feature movies we loved as kids, blast through this in an afternoon or evening, and have a good time doing it.