They are the second to last encountered of the four fractions in Half Life 2 (the others are Combine, human restistance and G-Man). They have access to considerable powerful fighting abilities and haven shown skills like teleporting (HL2:Ep1 Intro), powering devices, casting powerful bolts (one being strong enough to destroy Antlions, Zombies, Headcrabs…), freeing Gordon from G-Man’s control, keeping near-deaths alive and reviving them.
So why don’t we see more of them? Where have they been when we were batteling the Combine in City 17? Where have they been when we were defending White Forest? Hunting Advisors?
Why don’t they tell us something about the G-Man? They “worship” Gordon Freeman, but they don’t tell him anything about the nature of the one they freed him from. Maybe it is their nature to keep things ambigous.
What do you think are there interests? Do they want to live on earth after the war or would they return to Xen?