An interesting premise and some well-executed mecahnics overcome some of this games shortcomings.
The game is a mix of combat, adventure and puzzle solving. When it comes to melee combat, it is possible to target enemies and then attack certain limbs, which is most useful for decapitating zombies who will then roam around swinging randomly and potentially hitting their allies. This works farily well, though the movement can be a bit cumbersome when trying to avoid attacks, and then turn to target an attacker. This is because targeting freezes you in place, where a more free-roaming lock-on would have been preferred. Nevertheless, the system still works fairly well. All of the characters you play as will have access to melee weapons, though they will all be different and have different attributes, such as range or speed. Most of the characters will also have access to some form of projectile weapon, whether that be throwing stars when going back several centuries, or an assault rifle in the 1990's. The same targeting system can be used with the projectile weapons to take out enemies from afar. I used mine sparingly for fear of running out when I needed it the most, though I was probably more frugal than I needed to be.
Once the Tome of Darkness is found in her grandfathers mansion, Alex can begin her first chapter. The game design means the chapters must be played in order, and usually something discovered in each chapter offers Alex some way to further explore the mansion and find the next chapter page that are hidden around the mansion. Sometimes this can be a vision of something in the mansion, offering it for interaction when it had previously been unavailable. For example, learning the Enchant Item spell during one of the flashback adventures lets you repair a broken key that can be used to open up another part of the mansion.
Spellcasting is an integral part of the game. Runes can be collected, and then spells can be created by combining two runes, along with a third alignment rune. Codices must also be collected to learn the names of the runes, and spell scrolls can also be collected which will add that spell to your reportoire if you had not already learned it. Via game design you must collect all of the runes to progress, however it is possible to miss codices and spell scrolls. Unfortunately this led to some minor frustration later in the game when you have to prepare more powerful versions of the spells. If you don't have the spell scroll, it doesn't tell you how you made the original spell. Thus, you have to go through further trial and error to try and recreate it. The spells themselves can be fun to cast, but you have to make sure you are safe when casting them, as they take time to cast as runes appear on the ground as they are spoken aloud by an otherwordly voice; the more powerful the spell, the more runes it takes, and thus more time. The three different alignments work in a rock/paper/scissors fashion, thus choosing the right alignment can overcome obstacles that are aligned to its weakness.
As well as your health bar and magic bar, there is also your sanity to consider. This is a unique idea, and every time a character is seen by an otherwordly creature, they lose some sanity. Once an enemy has been beaten, it can usually be slain to restore the sanity loss it inflicted, although they only last for a short time before disappearing into the aether. If you lose all your sanity it can affect your health, however it is often worth losing your sanity just to see the effects that it causes. The most obvious effect is that the camera starts to tilt to one side, and becomes more severe the more sanity you have lost. Some of the more simple effects include blood seeping from walls or spiders appearing from nowhere, but there are some other effects that are very inventive. I'm loathe to give too much away as most of these are best discovered yourself, but at one point my character started sinking into the ground as though it were a gamebreaking glitch until it 'reset' to the last door I had entered, and my character gibbered that this couldn't possibly be happening. There was always something new in this department throughout the game, and it was a great way to mess with your head.
The puzzle solving comes from interacting with items, sometimes collecting them and then placing them in other locations. Other times certain spells would be required to overcome some obstacles. While most of these seemed obvious once the solution was in hand, I confess to having to use a game guide much more often than I would have liked which affected the pacing for me. However, others may not have this problem, or indeed prefer to be challenged by these puzzles. I also found a few times where I wasn't sure if I should have been continuing or not in case I missed something. In one particular case I was locked into a room and forced to fight a unique enemy with no effective melee weapon; the weapon was available if I had explored a different area first. As a result this fight took over 5 minutes of the same dodge and attack tactic before the enemy went down, and this was extremely tedious.
The story, setting and mood are the highlight of the game. The first chapter has you playing as Pious, who actually becomes your enemy. You will play as various characters through the ages, and each of them gives you a glimpse of how Pious is attempting to bring back an Ancient that will devour all of humanity, and their visions of the past bring you ever closer to the looming conclusion. As the title indicates, there is plenty of darkness here and it doesn't usually end well for our reluctant historical 'heroes'. The way the story is told via the chapters is very effective. On a few occassions you will find yourself revisiting the same area hundreds of years later as a different character with different options open to you, and areas that have changed as the centuries have passed. The enemies also add to the atmosphere. The most common is the zombie who lumbers about slowly, but can de dangerous in numbers if you get surrounded. A few other creatures out to wreak havoc on your sanity are lumbering horrors that can also cast spells, to trappers who can send you to another dimension and demons who will pounce on your head if they get close enough.
On a technical level, the game is adequate. It is obviously dated at this point, but nothing graphically stands out like a sore thumb. The lack of camera control is somewhat annoying, especially when you can hear enemies just ahead of you but you can't see them due to the chosen camera angle. The sounds of your enemies is effective, such as the sloppy sound of skinless zombies stepping across floors, and horrors howling after they have been defeated and crashing to the ground. The voice acting from the main characters got the message across, but did feel a little insincere at times.
Eternal Darkness has a few gameplay issues, but these are equally weighed by some interesting design choices (especially the sanity effects) and a compelling an interestingly told story. There may be better action adventure games, but there isn't one quite like Eternal Darkness.