Here is the full list of all 33 Half-Life 2: Update achievements. It takes around 8-10 hours to unlock all of the achievements on Windows.
Get the airboat.
Kill five barnacles with one explosive barrel.
Get the crowbar.
Break the mini-teleporter in Kleiner's Lab.
Escape the apartment block raid.
Hit the trashcan cop with the can.
Put the can in the trash.
Survive the rooftop strider battle in the ruins of City 17.
Escort Gregori safely through the church cemetery.
Cross the antlion beach in chapter Sandtraps without touching the sand.
Destroy the Citadel's reactore core.
Survive the generator plaza standoff in chapter Anticitizen One.
Play through Ravenholm using only the Gravity Gun.
Shut down the supression device by disabling its generators.
Get through the toxic tunnel under City 17 in Half-Life 2.
Survive the second turret standoff in Nova Prospekt.
Disintegrate 15 soldiers by throwing them into a Combine ball field.
Find all lambda caches in Half-Life 2.
Find the HEV Suit Charger faceplate in Eli's scrapyard.
Discover the hidden singing vortigaunt cave in chapter Water Hazard.
Gain command of a squad of rebels in the uprising.
Get the airboat's mounted gun.
Get the Gravity Gun in Black Mesa East.
Kill all of the snipers in City 17.
Destroy the Hunter-Chopper.
Use the Antlions to kill 50 enemies.
Kill 3 enemies using the crane.
Kill an enemy with a toilet.
Defend Little Odessa from the Gunship attack.
Use Dog's ball to make a basket in the scrapyard.
Pin a soldier to the billboard in the chapter Highway 17.
Destroy six gunships in Half-Life 2.
Kill five enemies with a Manhack.