With enough patience, you'll find an amazing and unique experience underneath the extreme difficulty.
The story of the game is simple enough to get a gist of at the start. There's a small cult in the middle of a forest near a Japanese village. Somewhere along the line, something goes horribly wrong and all the villagers are possessed by some malevolent force that turns them into homicidal maniacs. You'll play as a series of different characters using a time spreadsheet that connects each character and even allows them to fight through stages together. This form of storytelling alone is something I've never seen in a game, giving it a kind of Pulp Fiction view where the time line goes back and forth in order to make sense of earlier events or point out thing you might have missed the first time around. However, the voice acting isn't on par and some scenes tend to get awkward due to poor writing.
The graphics in this game are so-so in terms of character diversity and character models in general. While the faces are very realistic, it seems out of place with the rest of the character since they seem to have a sort of blocky feel to them. Still, it should be taken into consideration that this game was released in 2004 so it can be forgiven. Aside from the characters, the environments are nicely detailed and can be distinguished from one another to avoid confusion.
The gameplay is where the experience both shines and crashes. A few elements are well done but there are a fair share of flaws to point out. Thankfully, the pros decently outweigh the cons.
On the bright side, the ability to see through the eyes of your enemies (referred to as "Sight Jacking" in the game) gives you the chance to gauge your position with the enemy's. This is an incredibly useful tool and even shows if they're ready to attack or if they're simply waiting to ambush you. To find enemies to Sight Jack, you need to rotate the left analog stick like a radio dial as the static fades away to reveal an enemy's vision. It's also used as an alert system since the enemy's sight quickly flashes by when they see you so you can tell where they'll be attacking from.
Another shining gem comes from the general creepiness of the game. The tension the game manages to effortlessly build up leaves you terrified as you try to make it to the other end of the stage without being bludgeoned or shot to death. It combines both the Resident Evil "BOO!" scares and the atmosphere of Silent Hill quite well.
Sadly, there are a few drawbacks that drag this game down a couple points. The first of which is how you reload a weapon. Usually, you can walk and reload at the same time and it doesn't take too long. Unfortunately, the characters in Siren take roughly 2-5 seconds to reload their weapons and the reload is completely canceled if you take a step in any direction. This gets incredibly frustrating since it only takes the same amount of time for the enemies to run up and smack you to death.
Another draw is the incredible difficulty. There's no setting you can tweak for it and it only takes literally a couple hits for you to die from anything. In fact, some enemies only need to hit you once to kill you (or your horribly AI controlled partner in some cases). While this adds a unique trail-and-error element to the game, it becomes draining a few missions into the game.
Overall, Siren is a decently executed game with very unique elements that make it stand out from the usual horror giants. If you want an inventive, one-of-a-kind horror experience and you have plenty of patience, I highly recommend this game. However, those who couldn't stand the trial-and-error gameplay style that the Hitman series had, you'll definitely despise this game.