There are 10 levels with interesting puzzles that are of different kinds so it doesn't get boring. You get used to the things you should look out for fairly quick.

After finishing a level you unlock the next level and a harder difficulty option for the finished level.
The difficulty doesn't really make a difference as the puzzles do not get any harder (just other solutions and hints/objects are hidden in different places), but you do have less time.
However, time is never really an issue, which is good because the controls and the game itself (movement, interaction, crouching, inventory) feels kind of clunky and would not be fun if you really had to hurry.

Overall the game was good and a lot of fun.

There are 10 levels with interesting puzzles that are of different kinds so it doesn't get boring. You get used to the things you should look out for fairly quick. After finishing a level you unlock the next level and a harder difficulty option for the finished level. The difficulty doesn't really make a difference as the puzzles do not get any harder (just other solutions and hints/objects are hidden in different places), but you do have less time. However, time is never really an issue, which is good because the controls and the game itself (movement, interaction, crouching, inventory) feels kind of clunky and would not be fun if you really had to hurry. Overall the game was good and a lot of fun.