Here is the full list of all 33 Half-Life 2 achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Use the antlions to kill 50 enemies.
Destroy six gunships in Half-Life 2.
Get the airboat's mounted gun.
Get the airboat.
Kill five barnacles with one barrel.
Gain command of a squad of rebels in the uprising.
Get the Gravity Gun in Black Mesa East.
Find the HEV Suit Charger faceplate in Eli's scrapyard.
Destroy the hunter-chopper in Half-Life 2.
Get the crowbar.
Escape the apartment block raid.
Break the mini-teleporter in Kleiner's lab.
Discover the hidden singing vortigaunt cave in chapter Water Hazard.
Use DOG's ball to make a basket in Eli's scrapyard.
Play through Ravenholm using only the Gravity Gun.
Kill 3 enemies using the crane.
Pin a soldier to the billboard in chapter Highway 17.
Cross the antlion beach in chapter Sandtraps without touching the sand.
Kill an enemy with a toilet.
Survive the second turret standoff in Nova Prospekt.
Get through the toxic tunnel under City 17 in Half-Life 2.
Survive the generator plaza standoff in chapter Anticitizen One.
Kill all of the snipers in City 17.
Shut down the supression device by disabling its generators.
Survive the rooftop strider battle in the ruins of City 17.
Disintegrate 15 soldiers by throwing them into a Combine ball field.
Find all lambda caches in Half-Life 2.
Kill five enemies with a Manhack.