Managed to beat the game on Nightmare mode yesterday. For the most part it felt pretty similar to Hard difficulty, with the only major difference being the almost total lack of supplies given throughout the game. It was also pretty surprising how quickly flamethrower fuel could be used, but I never found myself running out. There also seemed to be a great amount of ethanol lying around, so I had plenty of Molotov cocktails on hand.
The only major difference I noticed with the Alien, besides the fact that second chances were taken out, was (I think) it could spot the light coming from the molotovs when I had them equipped. This could have been in my head though.
Had I gone from Medium to Nightmare I probably would have noticed a much greater change in difficulty, but currently Nightmare seems like a small step up from Hard.
