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.
Kill five barnacles with one barrel.
Disintegrate 15 soldiers by throwing them into a Combine ball field.
Survive the rooftop strider battle in the ruins of City 17.
Destroy six gunships in Half-Life 2.
Shut down the supression device by disabling its generators.
Kill all of the snipers in City 17.
Survive the generator plaza standoff in chapter Anticitizen One.
Get through the toxic tunnel under City 17 in Half-Life 2.
Gain command of a squad of rebels in the uprising.
Survive the second turret standoff in Nova Prospekt.
Use the antlions to kill 50 enemies.
Pin a soldier to the billboard in chapter Highway 17.
Kill 3 enemies using the crane.
Get the Gravity Gun in Black Mesa East.
Destroy the hunter-chopper in Half-Life 2.
Get the airboat's mounted gun.
Get the airboat.
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.
Find the HEV Suit Charger faceplate in Eli's scrapyard.
Use DOG's ball to make a basket in Eli's scrapyard.
Play through Ravenholm using only the Gravity Gun.
Cross the antlion beach in chapter Sandtraps without touching the sand.
Kill an enemy with a toilet.
Find all lambda caches in Half-Life 2.
Kill five enemies with a Manhack.