I wanna be the guy
Overview
Difficutly
There are four difficulty settings in the game: Normal, Hard, Very Hard, and Impossible. The main difference between the difficulties it the quantity of save points.
Walkthroughs
Adam Nelson is working on a walkthrough for the game. You can check out the latest version in this forum topic.
Neodraken has a full map of the game in this forum topic.
A list of the numerous video walkthroughs is maintained in this forum topic by catldr24.
UltraJMan has a let's play for this game in 50+ parts, the first part of which follows here:
<youtube>g3Xd21u3UDE</youtube>
There's a rather impressive (though incomplete) run of the left side of the game on insane mode by KyperTrast here:
<youtube>CPBgxWyXYKI</youtube>
Completed in a 3-part video by tijitdamijit: <youtube>pnllGJy7lSk</youtube>