That's not something you usually see in games of this type, but there's not enough of it to give it a lot of replay value. Good storyline, great graphics, good interface, but it is kind of short in the long run without a lot of replayability. Well, there's a lot of plot for this game. The manual does a good job of introducing it, and the game does kind of suck you in over time. In summary, you're ZAK, a 21st century hacker on a mission to infiltrate a secret base in Siberia, in search of some very ominous goings-on there.
Puzzle difficulty changes the puzzle difficulty.
Only two puzzles actually change dramatically, so it's not that big of a deal. Puzzle level, well, it's up to you, but levels 2 or 3 don't make that big of a difference. It's mood lighting. It's very helpful in some of the dark rooms and arcade sequences. Once you have arrived at The Rig, walk forward.