Jurassic: The Hunted

Here is some better tips for getting this achievement:
This doesn't have to be done in one playthru, you can reload any chapter from the main menu. Look for the ones with a skull on the picture in the botom left those are the ones you'll need to replay.

I'm going to explaine a few things while in hard mode.. you have to play thru on hard to get that achievement anyway and having the plasma rifle really does help a lot!

You can not unlock Hard mode without first finishing normal mode.. HARD mode is the only place you can find the plasma rifle and it will not cary over to normal even after you have beaten it on hard. There is no EASY mode.

Plasma rifle.. it's extremely hard to miss, but I guess if your just running thru you could perhaps miss it. Again (just for clarification.. start a whole new game on HARD from the beginning.. not 2 minutes or so in you will be prompted to examine a skeleton, if you’re looking at the skeleton the plasma rifle will be located on the same rock just a few short paces away at about the 11 o'clock position.. on the ground.

On Normal just walk thru the game.. don't run and gun or you'll get over whelmed and die. If you walk you'll be able to spot most dinos before they get to you and take them out.. Personally I meleed my way thru half the game including two Urharaptors and didn't die.. I just got careless at the balancing parts and fell in..lol..

Also be very careful at the MOUNTED GUN sequences these are the only parts that could really hurt you.. use your Adrenaline burst to give you and your gun a chance to heal/cool down. Use short controlled burst with the gun don't try to rush it, especially on the T-REX sequence or you will die. It's actually easier to do these sequences on normal than hard as you don't get to use any other weapons.

Normal you can get beat up pretty bad before dying and the T-Rex will have to bite you 3 times before you die, that's enough time to fend him off and heal up.. if he bites you 3 times your dead and have to start all over... but if he bites you twice the pterodactyls can kill you very quickly so again short controlled burst and good use of Adrenaline mode will ensure victory.

In hard mode anything kills you in 2 hits.. this makes the T-Rex sequence very frustrating. I can not stress the fact of short controlled burst and good use of the Adrenaline, also watch the pterodactyls shoot at the ones coming straight for you. Others look like they are getting close but they are off to the side's and will fly right past you and will not damage you, these are judgement calls you need to make, but it helps to not shoot everything that's close to you as your gun over heats pretty quickly on hard and on this level. One more thing 90% of the petrodactyls that will hurt you come from the right hand side but still be aware of those on the left.

For Hard mode, here is my advice and a trick that I have learned. Take it slow and steady plasma rifle rocks 1 - 2 hits for everything. On the parts when you have to defend your fortification ..don't even try to repair anything your just going to get attacked from the side or from behind and die. Instead do this:

Immediately go to the unlimited ammo box, (there is one in every one of these sequences.. tuck yourself up behind it so that you’re in the corner, No raptors will be able to attack you from behind or from one side.. they come at a pretty even pace so your plasma riffle should keep up with the reloading.. but here's the best part, if you’re in the corner backed all the way up as far as you can get, the raptors will not be able to hit you at all! They will run up to you, (and I mean right in your face!) but they won't attack.. all you have to do is fire your plasma rifle.

This works on all the fortifications sequences.. except there are two that you need to change your strategy just a bit.

The one where you need to place and explosive charge to clear the way: Get yourself in to the corner after a few raptors get in and you kill them they will stop coming.. but the music is still paying and you can hear one grunting.. it's stuck on the other side of the box your on. Quickly move around the box shoot it once and kill it, then get back into your corner and wait for more. Repeat this process as this will happen a few more times. This stuck raptor can also jump and damage you but he doesn't do that very often.

The last Fortification, (this trick will not work, the raptors can and will do damage to you, but it's still easy if you just do this: get into the same spot and the raptors will run right past you before attacking, giving you ample time to shoot them before they hit you. Just make sure to use one shot per raptor because they do sometimes bunch up but only about 3 at any one time. Using one shot per raptor will ensure that your plasma rifle will constantly reload/cool down.

SPIKE!
When you first get the animation of spike chomping at you from above wait there for him to go away. Continue on until you exit the small part of the tunnel. Upon exiting wait behind the small wall for a few seconds or you'll get run over by a herd of dino's.

After the herd passes follow the direction the herd went and on the right side you'll find the RPG. Ok now on to Spike!

*Don't try to use your plasma rifle on Spike.. it really doesn't do that much damage to him. Unless your you need to do a quick weapons switch.. (read on for that)

Spike has an animation where he will howl with pain and stop chasing you, this gives you time to reload and resupply your RPG, use your Adrenaline when you need to slow him down a bit and run a lot.. strafing him to keep him around the unlimited ammo box and just keep shooting him with your RPG.. if you miss quickly throw a few grenades at him. If he grabs you .. you don't have too much time so use Adrenaline and target his vitals.. if you run out of ammo while your upside down don't reload just switch to another weapon and keep firing!! He should drop you! If you wait or miss your dino food and will have to restart the chapter. I actually was picked up by him and got out of it on hard mode and then killed him a minute later. (but you don't have to do this chapter in hard you can just switch over and do it on normal which is a lot easier if your having trouble on hard for this particular part)

Edit update please read carefully:
This achievement seems a tad bit touchy and may seem to glitch on people, please read the comments below on how to continue on, I see that two gamers have tried clearing thief cashe and completely lost their save, so do this at your own risk and as a last ditch effort.

i had beat levels 1 -4 then came back and did 4 through the end of the game.. no cheevo.. so i went back and played levels 1-4 without exiting game (after beating 5 to the finish), and the cheevo unlocked. no need to watch cut scenes, just play it in one sitting and its not glitched or anything. i hope that was clear and saves someone some time.

Just play the game on Normal and play through it. If you died on any mission, you can come back once you have beaten the game and try again on that level you died on, as they are marked with a skull. They do not have to be done in any order, you just have to make sure no levels have a skull and your achievement should pop up.
Note: I do not know if playing on a different difficulty will affect this achievement.