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.
Make sure Gabriella is OK.
Kill a Witchbride using C4.
Party like it's 199.
Kill 20 enemies while dual wielding double shotguns.
Sign Secchi's rifle.
Kill 3 enemies with a double shotgun blast.
Head into Rome. Ditch Rodriguez.
Get a weaponized black hole, using science.
Kill 100 enemies with a headshot.
Run away from an angry volcano you foolishly antagonized.
Collect scorched aliens for Professor Kiesel.
Die HAARP With A Vengeance.
Kill 50 healthy Kleers with a direct double shotgun hit.
Recover the alien artifact located by Dr. Stein.
Kill an Aludran Reptiloid using nothing but a pistol.
One-shot kill 3 Werebulls with a shotgun.
Find out what happened to Alessandro.
Recover a key stolen by a cultist.
Kill a Belcher using Belcher collateral barf damage.
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.
Kill 5 enemies in a row while your health is below 10 HP.
Get knocked on the head and remember how you got here.
Meet a powerful granny.
Ride the Popemobile to victory.
Don't fear the reaper. Be the reaper.
Cross the French countryside and get very cross.
What if you could talk to the monsters?
Navigate the citadel of Carcassonne. Start reassembling your team.
Get justice. Get the Holy Grail. Get screwed over.
Escape the Oil Rig.
Send Mental a message he won't forget.
Beat the game on any difficulty.
Unlock 10 S.A.M.s in a single playthrough.
Destroy 10 propaganda drones.
Melee a big enemy.
Kill 5 enemies during a single Time Warp slowdown.
Use the mininuke to eliminate 100 enemies at once.
Kill 11 different enemies using melee attacks.
Make 20 enemies kill each other using Psychotropic Grenades.
Spend 1000 minigun rounds while firing continuously.
Harvest 100 enemies with a combine harvester.
Dismember 50 enemies with cannonballs.
Assist Dr. Vermetti in his war on worms.
Find out what happened to the English airman.
Assist a couple of young ladies out hunting.
Discover Fulbert's great invention.
Protect humanity's treasures from invaders with no taste.
Achievement is your middle name.
Save a princess. Doesn't get more classic than that.
Go on a date with Hellfire.
Finish a text adventure. On an oil rig. During an alien invasion.