This is a guide to make things a little easier whilst playing on "Predator" difficulty.
If you want to make things a little easier then use the following codes (put in via Cheats Menu). "Bloodlust" and "UnleashHell" these need to be only put in once while playing (These become available as you get upgraded). "ImJackCarver" 100 health. Must be put in everytime your low (which will be a lot).
OK the rest of the "Tips"
1. Unless you're a hero play through on a lower level first. Achievements don't stack and you'll need to know the maps as there is NO RADAR on this mode.
2. Take your time when clearing areas, its not unlimited spawns and eventually everyone will die ... leaving you time to recompose.
3. Have a go at heading straight for the checkpoints (you won't always have to kill everyone)
4. Watch out for Snipers .. they are 2 shot kills
5. In river sections don't use Boats / Jetski's .. just swim at the bottom of the river and pop up for air in the clear areas where you won't get shot. This can save hours of work.
6. In areas where there are no snipers or you have already got rid of them use 2x Machine Guns. Start one off and when it gets half way down start the other and hold both triggers .... that way at least one is always firing.
Some parts are more tricky than others, here are just a few of them.
Looking after Val.
You'll get to a cliff overlooking a dock area with Val on it. Take out the sniper on top of the cliff and get ready to tear your hair out. There are about 8 guys that are trying to kill Val and you need to snipe them all (before she dies). I didn't zoom right in as it made it difficult to see them all running. Kill the ones at the front 1st.
The Big Fat One Armed Blobs.
They move pretty slow and as long as you've got "Bloodlust" switched on just keep running around them. You need to get behind them and slash at them (Mash the B Button) a few times then back off before he clobbers you. Do it a couple more times and it'll die.
The Swamp Area.
In the swamps there are 3 snipers in one section. Have a few goes to work out exactly where they are at (2 on platforms and 1 at the end near the fire) and make sure you take them out .. otherwise they WILL get you.
You'll be in a corridor with 3 enemies (1 sniper and 2 gunners). Run past the 1st guy and "slash" the next two. Don't kill the last guy just yet as Doyle will not move and is safe. Then look at the back of the room and go through the door and up the stairs, kill that guy. When you come back down the other guy might be there .. try and scare him into running away. When you get into the room where the sniper was shoot him and then 4 more will spawn outside the door (1 sniper and 3 gunners). Try and get them and then run back into the building and get the guy following Doyle. Once your back outside get rid of everyone as quick as possible and head to the next check point. If Doyle has less than 100 health (more than likely) just die and when you restart he'll have 100 health and will then wait in the room next to the checkpoint. After that its just about clearing the enemies outside and making sure he gets into the helicopter.
Final Boss Battle.
With "Bloodlust" on I didn't fire a single shot till I got rid of all the goons jumping down. Just run at them and "slash". Once they are all done shoot at Crowe till he jumps down. Then do the same to him. Took less than 2 minutes and did it on my 1st try.
Like I said earlier in the Tips most of it is just run to the next spawn point, but here are a few that I could remember where you must clear out 1st.
At the point where Crowe lands on top of a building in his helicopter and you need to jump over the wall into an area with Cargo Crates.
.... Just go straight to the left and stand in the corner. You'll get 4 or 5 waves of screaming zombies running at you. Shoot them all with the 2x Gun method. It'll say "Crowe is retreating" (Top left of screen) when your done and a tower will crash down to let you climb over the wall.
When you enter the building which has 4 guys in a darkened room (B Slash them all), jump over the boxes and run straight ahead to the 2 closed doors. Stand in the corner and just shoot em all till no one is left.
When The Lift Opens (Just after above bit)
2x Gun them all and stay in the lift. When it goes quiet move down the corridor and run into the kitchen. Head for the cupboard in the corner and get the armour and lay down. Shoot em all till you hear a crash, thats the point you can go up stairs for the Final Boss Battle.
Hope this helps. Enjoy