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.
Unlock 10 S.A.M.s in a single playthrough.
Get justice. Get the Holy Grail. Get screwed over.
Make 20 enemies kill each other using Psychotropic Grenades.
Kill 100 enemies with a headshot.
Go on a date with Hellfire.
Navigate the citadel of Carcassonne. Start reassembling your team.
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.
Don't fear the reaper. Be the reaper.
Destroy 10 propaganda drones.
Harvest 100 enemies with a combine harvester.
Assist a couple of young ladies out hunting.
Kill 20 enemies while dual wielding double shotguns.
Find out what happened to the English airman.
Ride the Popemobile to victory.
Kill a Belcher using Belcher collateral barf damage.
Meet a powerful granny.
Make sure Gabriella is OK.
Party like it's 199.
Sign Secchi's rifle.
Kill 5 enemies during a single Time Warp slowdown.
Get a weaponized black hole, using science.
Head into Rome. Ditch Rodriguez.
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.
Recover the alien artifact located by Dr. Stein.
Find out what happened to Alessandro.
One-shot kill 3 Werebulls with a shotgun.
Recover a key stolen by a cultist.
Kill 5 enemies in a row while your health is below 10 HP.
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.
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.
Kill a Witchbride using C4.
Dismember 50 enemies with cannonballs.
Assist Dr. Vermetti in his war on worms.
Discover Fulbert's great invention.
Finish a text adventure. On an oil rig. During an alien invasion.