*EDIT* So for this to unlock you need to complete the game on Normal or Hard difficulty, which then unlocks Inhuman difficulty and this achievement. *END EDIT*
Tips for surviving this game:
Stay in cover.
Knife creatures whenever you can, it makes you invulnerable during the knife kill animation.
Sniping keeps you from getting shot up close.
Using the mini gun as a turret adds another gun against the enemy and allows you to move around while the enemy continues to take damage.
Focus on making it from save point to save point, don't be discouraged if you die.
Holding the knife makes you run faster than holding other weapons.
For the first T Rex fight, run to the tree in the middle (that lets you use it as cover) and stay in there while you lay the fire into the Rex.
For the fight with the Beast, use the gas vents in the ground (with the steam coming out) and the flame thrower to inflict damage on him every time he lunges at you. Keep up against the wall so that his tentacle swing misses you. Keep running when he starts throwing rocks at you.
For the last boss fight, use a set of crates in the area to circle around while the Boss circles around it as well trying to chase you. The weapon of choice doesn't matter, as long as you continue to use the shotgun flare to distract him, and then use whatever weapon on him, and continually circle around. The circling prevents him from catching up to you since his speed is faster than yours. Use the youtube link if you need more help.
Props to lawlessSaturn for posting this video on youtube.