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.
Get justice. Get the Holy Grail. Get screwed over.
Go on a date with Hellfire.
Dismember 50 enemies with cannonballs.
Kill an Aludran Reptiloid using nothing but a pistol.
Recover a key stolen by a cultist.
Destroy 10 propaganda drones.
Kill 100 enemies with a headshot.
One-shot kill 3 Werebulls with a shotgun.
Kill a Belcher using Belcher collateral barf damage.
Navigate the citadel of Carcassonne. Start reassembling your team.
Make 20 enemies kill each other using Psychotropic Grenades.
Save a princess. Doesn't get more classic than that.
Spend 1000 minigun rounds while firing continuously.
What if you could talk to the monsters?
Achievement is your middle name.
Cross the French countryside and get very cross.
Kill 20 enemies while dual wielding double shotguns.
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.
Kill 5 enemies during a single Time Warp slowdown.
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.
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.
Get together with your friends and kill something big.
Fight alongside Massimo Murena.
Unlock a S.A.M.
Kill 5 enemies in a row while your health is below 10 HP.
Save the rookie. Find Father Mikhail. See the sights.
Kill 3 enemies with a double shotgun blast.
Get knocked on the head and remember how you got here.
Unlock 10 S.A.M.s in a single playthrough.
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.
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.
Protect humanity's treasures from invaders with no taste.