Incredibly immersive, with some flaws.
The first thing to note is that to truly be immersed, you have to let yourself. It isn't Dead Space, where you're running around eager to tear some limbs off of a freaky alien monster. Don't charge down hallways just because you know the worst that can happen is you have to respawn from a checkpoint. Take it slow, cut the lights, and let yourself enter Daniel's shoes.
Before buying this, note that it is not a "fun" game in the traditional sense of the word. The gameplay and controls are really quite bland. Nor is it a game with high replayability. It's more of a challenge to beat and a great game for thrill seekers.
The game does manage to combine some good survival elements in it - you have a limited supply of oil, which is hard to find, and tinderboxes, which are somewhat more common but still rare. This leaves you being very particular about your light use - however, your sanity drops when you are in the dark, so you have to use your resources right.
My only complaints about this game are minor. The graphics are a little outdated, and sometimes the puzzles toe the line between challenging and annoying. The game is somewhat short, but then again this varies on how much time you spend crouching in a corner or tearing apart rooms looking for lantern oil. Finally, I would like to see a greater amount of enemy encounters - while one of the game's strengths is that it manages to make you feel like you're always in danger even though you are more often than not safe, adding a few more moments of terror would make this game golden.
But still, for only 20 bucks, this is definitely worth a play.