1. G-Man Sightings
The mysterious G-Man can be seen in various background locations throughout the game, often observing Gordon from a distance. Keep an eye out in City 17, during the teleportation sequence, and even in the Citadel.
2. Half-Life 1 References
Dr. Kleiner's lab is full of references to the original Half-Life, including a picture of a Headcrab named 'Lamarr' and various Black Mesa artifacts. Barney also mentions his debt to Gordon from Black Mesa.
3. Developer Commentary
For a deeper dive into the game's development, enable 'Developer Commentary' from the main menu. This adds floating commentary nodes throughout the game, offering insights from the creators.
4. The 'Lambda' Symbol
The Lambda symbol (λ), representing the resistance, is often painted on walls or hidden in the environment. Finding these can sometimes lead to hidden supply caches.
5. The Singing Vortigaunt
In 'Black Mesa East', if you linger in the area with the Vortigaunts, one of them will occasionally sing a unique song. It's a small, charming detail.