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.
Finish a text adventure. On an oil rig. During an alien invasion.
Get justice. Get the Holy Grail. Get screwed over.
Dismember 50 enemies with cannonballs.
Go on a date with Hellfire.
Navigate the citadel of Carcassonne. Start reassembling your team.
Kill a Belcher using Belcher collateral barf damage.
Make 20 enemies kill each other using Psychotropic Grenades.
Save a princess. Doesn't get more classic than that.
Kill a Witchbride using C4.
Kill 100 enemies with a headshot.
Kill an Aludran Reptiloid using nothing but a pistol.
One-shot kill 3 Werebulls with a shotgun.
What if you could talk to the monsters?
Achievement is your middle name.
Melee a big enemy.
Protect humanity's treasures from invaders with no taste.
Cross the French countryside and get very cross.
Kill 5 enemies in a row while your health is below 10 HP.
Don't fear the reaper. Be the reaper.
Assist a couple of young ladies out hunting.
Ride the Popemobile to victory.
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.
Head into Rome. Ditch Rodriguez.
Kill 5 enemies during a single Time Warp slowdown.
Get a weaponized black hole, using science.
Run away from an angry volcano you foolishly antagonized.
Kill 20 enemies while dual wielding double shotguns.
Collect scorched aliens for Professor Kiesel.
Die HAARP With A Vengeance.
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.
Kill 3 enemies with a double shotgun blast.
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.
Destroy 10 propaganda drones.
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.
Discover Fulbert's great invention.