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.
Beat the game on any difficulty.
Escape the Oil Rig.
Finish a text adventure. On an oil rig. During an alien invasion.
Unlock 10 S.A.M.s in a single playthrough.
Get justice. Get the Holy Grail. Get screwed over.
Go on a date with Hellfire.
Dismember 50 enemies with cannonballs.
Navigate the citadel of Carcassonne. Start reassembling your team.
Kill a Belcher using Belcher collateral barf damage.
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.
Discover Fulbert's great invention.
Don't fear the reaper. Be the reaper.
Assist a couple of young ladies out hunting.
Ride the Popemobile to victory.
Destroy 10 propaganda drones.
Make 20 enemies kill each other using Psychotropic Grenades.
Meet a powerful granny.
Assist Dr. Vermetti in his war on worms.
One-shot kill 3 Werebulls with a shotgun.
Make sure Gabriella is OK.
Kill 100 enemies with a headshot.
Kill a Witchbride using C4.
Party like it's 199.
Kill 20 enemies while dual wielding double shotguns.
Sign Secchi's rifle.
Head into Rome. Ditch Rodriguez.
Get a weaponized black hole, using science.
Run away from an angry volcano you foolishly antagonized.
Kill 5 enemies in a row while your health is below 10 HP.
Collect scorched aliens for Professor Kiesel.
Die HAARP With A Vengeance.
Kill an Aludran Reptiloid using nothing but a pistol.
Kill 5 enemies during a single Time Warp slowdown.
Recover the alien artifact located by Dr. Stein.
Kill 3 enemies with a double shotgun blast.
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.
Save the rookie. Find Father Mikhail. See the sights.
Get knocked on the head and remember how you got here.
Melee a big enemy.
Use the mininuke to eliminate 100 enemies at once.
Kill 11 different enemies using melee attacks.
Kill 50 healthy Kleers with a direct double shotgun hit.
Spend 1000 minigun rounds while firing continuously.
Harvest 100 enemies with a combine harvester.
Find out what happened to the English airman.