CountessRae
says
Invader Zim is Half-Life. Dib is Gordon Freeman. The Irkens are the Combine.
The Vortigaunts are any of the alien races enslaved by the Irken empire
Zim would be a very incompetent Combine Advisor
Gaz is Alyx
the Meekrob would've been G-Man
all the rebels in Black Mesa East would be The Swollen Eyeball I guess