Here is the full list of all 54 Serious Sam 4 achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Send Mental a message he won't forget.
Escape the Oil Rig.
Unlock 10 S.A.M.s in a single playthrough.
Get justice. Get the Holy Grail. Get screwed over.
Dismember 50 enemies with cannonballs.
Go on a date with Hellfire.
Save a princess. Doesn't get more classic than that.
What if you could talk to the monsters?
Achievement is your middle name.
Protect humanity's treasures from invaders with no taste.
Cross the French countryside and get very cross.
Kill 5 enemies during a single Time Warp slowdown.
Don't fear the reaper. Be the reaper.
Assist a couple of young ladies out hunting.
Ride the Popemobile to victory.
Spend 1000 minigun rounds while firing continuously.
Make 20 enemies kill each other using Psychotropic Grenades.
Meet a powerful granny.
Assist Dr. Vermetti in his war on worms.
Make sure Gabriella is OK.
Party like it's 199.
Sign Secchi's rifle.
Kill 20 enemies while dual wielding double shotguns.
Head into Rome. Ditch Rodriguez.
Get a weaponized black hole, using science.
Run away from an angry volcano you foolishly antagonized.
Collect scorched aliens for Professor Kiesel.
Die HAARP With A Vengeance.
Kill an Aludran Reptiloid using nothing but a pistol.
Kill 5 enemies in a row while your health is below 10 HP.
Recover the alien artifact located by Dr. Stein.
Find out what happened to Alessandro.
Recover a key stolen by a cultist.
Get together with your friends and kill something big.
Fight alongside Massimo Murena.
Unlock a S.A.M.
Kill 3 enemies with a double shotgun blast.
Save the rookie. Find Father Mikhail. See the sights.
Get knocked on the head and remember how you got here.
Navigate the citadel of Carcassonne. Start reassembling your team.
Beat the game on any difficulty.
Destroy 10 propaganda drones.
One-shot kill 3 Werebulls with a shotgun.
Melee a big enemy.
Use the mininuke to eliminate 100 enemies at once.
Kill 100 enemies with a headshot.
Kill a Belcher using Belcher collateral barf damage.
Kill 11 different enemies using melee attacks.
Kill 50 healthy Kleers with a direct double shotgun hit.
Harvest 100 enemies with a combine harvester.
Kill a Witchbride using C4.
Find out what happened to the English airman.
Discover Fulbert's great invention.
Finish a text adventure. On an oil rig. During an alien invasion.