Half Life- Grenades are a great way to introduce yourself. If you're nervous about going into a room, ventilation duct, or crowded area, just throw Mr. Pineapple out there, and wait a second. Now that you've been introduced to the room, stroll in with confidence!
Also- yes, there is a headcrab there. There is always a fucking headcrab there. Doesn't matter where, there is a headcrab hiding SOMEWHERE. Even if there's no possible way for a headcrab to be hiding where you're talking about, the game will say "Oh well fuck you then" and teleport one in mid-leap to bite you out of nowhere.
Also- the "Barneys" don't really understand the concept of "friendly fire". If you're in the way of them and what they want dead, well then sucks to be you.
Also- Noclipping through the first section of the game is actually slower than straight-up taking the tram. The tram can move faster than you can noclip.
And... that's about it. I'm playing through it a fourth time, just to make sure I did everything I could.