Achievement: Black Mesa
Description: Get to Black Mesa.
Achievement: H.E.V Science.
Description: Get the Black Mesa H.E.V Suit.
Achievement: Time?
Description: Ruin the universe.
Achievement: GIVE ME THE SODA!
Description: Break a soda machine.
Achievement: Firearms
Description: Get a pistol.
Achievement: Kill them all!
Description: Kill your first enemy
Achievement: Exploding Zombies
Description: Get a grenade.
Achievement: Figures..
Description: Die for the first time.
Achievement: Is it time Mr. Freeman?
Description: See GMan for the first time.
Achievement: No regrets, Mr Freeman.
Description: Decline GMan's request and get the bad ending.
Achievement: The 7 Hours.
Description: Accept GMan's request and get the good ending.

If you want some achievements added. Please say so in the comments.