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.
Go on a date with Hellfire.
Dismember 50 enemies with cannonballs.
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.
Discover Fulbert's great invention.
Don't fear the reaper. Be the reaper.
Assist a couple of young ladies out hunting.
Find out what happened to the English airman.
Ride the Popemobile to victory.
Make 20 enemies kill each other using Psychotropic Grenades.
Meet a powerful granny.
Assist Dr. Vermetti in his war on worms.
Kill 100 enemies with a headshot.
Make sure Gabriella is OK.
Kill 11 different enemies using melee attacks.
Party like it's 199.
One-shot kill 3 Werebulls with a shotgun.
Melee a big enemy.
Kill 5 enemies in a row while your health is below 10 HP.
Sign Secchi's rifle.
Kill a Witchbride using C4.
Head into Rome. Ditch Rodriguez.
Kill 3 enemies with a double shotgun blast.
Get a weaponized black hole, using science.
Kill 20 enemies while dual wielding double shotguns.
Kill 5 enemies during a single Time Warp slowdown.
Run away from an angry volcano you foolishly antagonized.
Collect scorched aliens for Professor Kiesel.
Die HAARP With A Vengeance.
Recover the alien artifact located by Dr. Stein.
Kill an Aludran Reptiloid using nothing but a pistol.
Kill a Belcher using Belcher collateral barf damage.
Find out what happened to Alessandro.
Recover a key stolen by a cultist.
Get together with your friends and kill something big.
Spend 1000 minigun rounds while firing continuously.
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 50 healthy Kleers with a direct double shotgun hit.
Harvest 100 enemies with a combine harvester.