Learn, adapt, experiment and survive.
Amnesia: The Bunker is an excelent Survival Horror game that gets to the point with a simple, but effective and well executed premise. Play as a soldier trapped in a WW bunker, who must explore, gather and manage resources, and open an escape route while surviving a deadly monster that lurks in the dark waiting for you to be his next victim.
Compared to previous entries in the Amnesia series, it might not be as heavily focused on the horror experience or the story. This focusses on gameplay mechanics and replay value instead. Whether you find that better or worse it's up to you, I personally consider it a good thing because from what I've seen I found the previous Amnesia games rather "empty" and with very little to offer in terms of gameplay, even if they might beat this one in other aspects.
The Positive:
Survive the horror, by using your brain and tools to navigate through the bunker searching for a way out, while doing your best to avoid the monster that's waiting for his chance to kill you. You have access to a few weapons, types of grenades, and other utility tools you can find or craft. You can somewhat fight back, although the stalker cannot be killed until the end of the game, so while you have tools to distract or temporarily make him retreat, keep in mind that those resources are limited so, especially in higher difficulties, you should think carefully how and where you use them. Think of it as a shorter, more condensed, version of Alien Isolation (probably the closest experience to it).
Overcome obstacles in multiple ways. Most tools, and "problems" you find (rats, traps, locked doors, etc.) have more than one way to interact or be dealt with. Judge, experiment and decide what would be the best course of action for your survival depending on the circumstances, what you've found, and what you need.
No two playthrougs are the same. The majority of resources, Lockers, Codes, Traps, Rat spawns, Inventory expansions, etc. are randomized at the beginning of each playthrough, so there's no fail-safe route to success in this game as the same room that was a waste of time to check on your previous run might give you something very useful in the next. Adapt and do your best with what you have.
Generator management. A very important mechanic that makes the game more unique. You can fill the Generator with Fuel canisters you find scattered across the game. While the generator is turned on so will be the lights, and the stalker isn't a fan of lights, which means he might not bother you unless you provoke him or give away your position by making loud noises. While the lights are off, he'll be allowed to randomly come out and patrol just because he feels like, making your exploration a lot more dangerous. This adds to the importance of decision making and resource management, as the generator drains fuel on a timer basis, and there are other uses for fuel too, so at least in higher difficulties (where Fuel drains faster) you need to think strategically which tasks you can do in the dark to save some fuel for other tasks where you totally need the generator turned on.
Extremely customizable difficulty that adds even more replay value. On top of the four base difficulties (Easy, Normal, Hard, and Shell Shock), you can also create your custom difficulty by adjusting individual parameters. Want to have the most terrifying stalker possible, but no rats and a much bigger inventory? You can do that. Balance and customize the experience however you wish with over 30 different settings.
The Negative:
Optimization is terrible, apparently due to the game running on a very old engine. Even if you're past the recommended requirements, don't expect to be able to run this game at steady FPS on highest quality graphic settings because the game/engine is just not ready for it. You'll most likely have to turn off or lower certain graphic options.
Randomization is a double-edged sword. A lot of the challenge in this game comes from its heavy RNG, which you can trivialize by saving/loading. Got a Code for a locker but died? Well, you can reload and open the locker without having to repeat the area where you found the code, because you already know it. So there are quite a few tasks you can cheese or even outright skip through this method, of course unless you choose not to. It's up to you how you want to play but the option is there.