Hi im on the level where you have to ambush this ship to get on it and save some guy. The one where your given a sniper rifle to take out all the gangs of aliens.

I fought off the last gang but i don't know how to get to the ship, is their some path or do you have to clibm up that massive cliff?

You might have missed the little passage through the rock face around the upper edges. Go through their and another large battle takes place, finishing with the slaughter of two Hunters which beam down the spaceships portal (in the center.) After that you will receive reinforcements and move yourself onto the portal platform and you will be beamed up to the ship. Sorted