Trivia: In the first level (Time To Split) when Cortez is holding off the Time Splitters with the gun emplacement one of the soldiers says "They're coming out of the walls! They're coming out of the goddamn walls!" A quote from from "Aliens."
Trivia: In the eighth level (You Genius, U-Genix), after you get the disguise, Amy says "Remember, your name is Gordon now. Lead the way, doctor." This is a reference to Half-Life's main character Doctor Gordon Freeman.
At the end of the second level (Scotland The Brave) Cortez picks up a photograph of Crow and Khallos. In the next level (The Russian Connection) you see the picture being taken, and Crow and Khallos have switched places.