I'm writing this guide for the Hard difficulty. Hard in this game is pretty easy compaired to Hard difficulty in other games.
You've landed on an Orc ship. You need to take this thing out, and then make it to the planet's surface.
Several gretchen will attack you here. Your gun has infinite ammo so you might as well send some bullets their way. When your clip is empty, just hit R2 to reload.
These enemies are so weak you can just press circle to kill them.
Eventually two orcs will show up. You can take them out with your knife, or try shooting them. The knife was easier for me.
You can also press triangle to stun them, and then press circle to kill them. Doing that will recover some health if you happened to lose any.
Another group of orcs will rush you. There will be more of them this time. Throw bullets at them as you are walking backwards. Orcs do not move fast. You can kill a lot more of them on a fighting retreat.
You will have to mop up a couple with your knife. Be sure to stun them(triangle) and then execute(circle) them to regain any lost health.
Reload and move forward. To your right an orc gunner will appear. Next to him is a bomb. Shoot the bomb to take out the gunner.
Once again, a common theme for this game, orcs will rush you. Fighting reteat while you pump shells into them.
After killing that group of Orcs and Gretchen, move forward.
The ground will explode in front of you. Work your way to the right after the explosion.
There will be a shooter, and a bunch of regular orcs coming at you. Once again a fighting retreat will serve you well here.
After that batch of orcs, move forward. You will see a shooter next to a bomb on your right. Shoot the bomb to take him out.
The bomb will blow up the pipe that is blocking your way. When the pipe is gone you will see a couple more shooters along with a couple regular orcs. They will not run forward. So take out the shooters first and then take out the other orcs.
As you move forward you will see a cut scene with the Orc Warlord in it.
Several shooters and a wave of orcs will rush you here. If possible take out the shooters first, and then do another fighting retreat to clear the orcs that are heading your way.
This wave of Orcs will be slightly larger than the ones you've seen before. So keep retreating and dumping shells into them.
There is a bomb close to the big guns on this ship. Shooting it will take out a shooter or two.
You will be rushed by a second wave of orcs. These will be a lot easier because they will not have shooters with them.
A fighting retreat will work very well on these orcs.
After those orcs are cleared, move up to the big gun. You will see that there is a gear symbol on the front of it.
Press the button to grab the gun and turn it towards the ship.
The gun will blow up the ship, and you will eventually end up on the ground.