In answer to the latest babble...
Half-Life 1 WAS good in it's hay-day, the original now is really out-of-date but with people coming out and adding hi-def models and textures we continue to push the HL engine. I think the HL engine is equally as powerful as the HL2 engine BUT the HL2 engine was built to cover a wider base so allows more effects. I've seen very HL2 maps in Half-Life 1 look almost up to scratch, but anyway, you'll all yell at me now for saying that...
I can't even buy Quake 4 anymore, i can't find it anywhere, Quake Wars look much better anyway.
As for Ninilith, this is my theory:
Ninilith was the central being for the xen race which was much more diverse than they actually were able to show in HL1. Ninilith communicated via telepathy to all his minions. The alien grunts and islaves were his personal slaves, who were forced to do his bidding, if they didn't their collars they wear, which are restraint devices, would kill them. Look in the slave's model animations, you can see one where they cower in pain because they did wrong. When Ninilith was killed by Gordon, the Xen race was in choas, without a leader. These other Xen beings called Advisors (in HL2) moved up and took over the leadership but they had their own plans and tried to kill all the old xen creatures to build their own empire, hence why the alien slaves (now call vortigaunts) are free because they escaped. The Advisors captured humans and turned them into the combine which they used to attack earth and won in seven hours after Dr Breen surrendered Earth to them. That's my thoery