Samantha Wins

I think you can finish the game without doing it, but you can examine items in your inventory with the [I] key. Once you have the glasses it'll reveal more details about the story and explain some of the imagery.

Yeop, totally forgot I had an inventory. Never opened, so yes you can finish without opening it, but I don't know if the result changes. You probably get more "achievements" if you open the inventory. It may also give more hints at the plot earlier on.

Hmmm. First time I played through, I had an option to do something with the car. I figured that would lead to the end of the game, and so I didn't, and went through the rest of the game, but didn't have an option to go back to the car. So, I played through again, but this time didn't have an option to do anything with the car. I don't know what I did differently (other than using the inventory as other folks have mentioned).

There's a meaningful message and a very emotional story, but the game mechanics themselves are nothing any more than walk around and press 'Space' until something happens. Plus, the eerie parts of the game could've been taken out and made the game more meaningful - otherwise it's just comes across as trying to be a scary game, which I don't see it as.