Don't need them, seeing as how I've already beat the game. :-P
What was your favorite level in the game? For me, it's a toss-up between "We Don't Go to Ravenholm" (for the sheer creepiness/atmosphere factor), "Nova Prospekt" (Come on. ANTLION HORDES AT YOUR COMMAND!), and the final two levels of "Our Benefactors" and "Dark Energy" (for the eerie Citadel's inner workings, the super Gravity Gun, and the admittedly cool ending).
"Follow Freeman."
Taking out those Striders is a blast!