Here is the full list of all 49 Serious Sam: Siberian Mayhem (Windows) achievements worth 1,000 gamerscore.
No complaints. Only skills
Back on the mainland
Anything for a reward
In Mother Russia, you invade the aliens!
Set your spirit free
Through the snow, flames, and alien bodies
Embrace the origins
Searched for the enemy, found new friends
From Russia with love
Meet the naughty monster
Try a new career
No hope for a hopping mob
A tooth for a truth
When passion becomes profession
When passion overcomes the pain
A solution to any problem
The smartest man on Earth
You are here to shoot, right?
From granny, with love
Hey, this looks familiar!
Find every Dmitry audio and text log
Find all of the print media notes
Find every General Brand audio log
Now it's your turn
Rise and levitate
Defeat Sentry Tower with sole hoverboard firepower
Stay here and kill them all... with a black hole
Kill 10 enemies with one Burner explosion
Kill Draconian Burner with a Burner gun
Kill 30 enemies while riding one Draconian Burner
Kill 5 enemies with one Crossbow shot
Complete the mech sequence and kill all big enemies without shooting
Don't ride the tank - become the tank
Beat the final boss in Singleplayer on Serious difficulty without loading mid-battle savegames
Complete Siberian Mayhem without learning a single S.A.M skill in Singleplayer
Complete Siberian Mayhem on Serious difficulty in Singleplayer
Complete Siberian Mayhem on Serious difficulty in co-op with enemy multiplier set to at least x2
Rid the monster of its misery
...at least once
Not the best way to keep warm
Find half of all the secrets
Find all secrets
Get any medal on Castle of Pain survival level
Get any medal on Horus Sanctuary survival level
Get any medal on Kleer Fortress survival level
Get any medal on Dragon Gates survival level
Get any medal on The Snowrider survival level
Get any medal on Monkey Canyon survival level
Get a gold medal on any survival level