I finished Chapter 8 last night, which was the hardest chapter I've played yet. I'll explain below in spoiler tags for anyone who'd like to know. In my spoilers are also some of my tips to succeeding it.
Spoilers:
In Chapter 8 you encounter a new type of zombie-type enemy. They're capable of vomiting acid at you, they bite when they grab you and you can't stealth kill them. They've got two kids, so if you head shot one head, it might still be standing. They're a pain in the arse.
I found that this area has a lot of traps (not the disarmable kind) that you can use against these guys to conserve your ammo. I think that's what this area is trying to make you do, because in this chapter you can hardly use stealth, as it's quite linear.
The boss, who is "The Keeper" or "Box Head" as he's known on the Internet is a huge dude with a big arse hammer. Before you fight him, you have to run down a corridor filled with this land mine trap things, if you step on one, it wraps barbed wire around your leg and traps you. Mean while, as you run through this corridor, the ceiling is falling with spike traps. So you can't step on one or else your dead.
I found I couldn't beat the Keeper because of my lack of ammo... so I actually restarted the chapter from a previous save file and re-did it, using the traps against enemies and conserving my ammo. I did use my gun (mostly sniper rifle) sometimes but I saved what I could, mostly cross bow bolts.
When you fight the Keeper, you have to fight him in stages. There's also poisonous gas in the area slowly killing you, which you can slow down by turning off nearby valves (but it makes you vulnerable to the Keeper and his possible one hit kill attack).
The first stage is straight forward, again hopefully you've saved some of those cross bow bolts. I used a freeze bolt, followed by a grenade and that took care of him. I went into the next room and had to "fight" him again, but it turns out you don't have to. Grab the loot on the table, then run through the open vault looking door. Sebastian will immediately and automatically close it behind him, which brings you to the third stage. Here, you've gotta fight him and I'd recommend using the freeze bolts and explosive bolts, maybe the shotgun too if you have shells.
You then will move onto the forth stage, again here you don't have to fight him. What you will have to do though is grab a valve wheel to close off the gas, because the Keeper destroys it as you enter the room. You can find it on a nearby table. Once you've done this, you can honestly just leg it. You'll find a set of stairs (or a corridor, I forget) that will lead the Keeper to a trap which if you succeed, will finally kill him.
End spoilers:
In Chapter 9, there's something very obvious players will see and remember. Sebastian comments, "I've seen this before, but where..." - when you see it, you'll know exactly what it is. I think it's a forth wall thing, almost a joke or a homage at least.