"Summer Camp, Florida", "Salvage Yard, Mojave Desert", "Asylum Station 2 - Experimentation Rooms" - Restored Levels. (Cut content)
Yort, Seraph Queen - Restored bosses (Cut content)
Seraph - Restored enemy (Cut content)
Tete de Mort - Weapon (Not sure if this was originally cut content)
Restored voice lines (Cut content)
The Horror difficulty (Added for Remaster)
NG+ mode (Added for Remaster)
A reward for collecting all dark souls and cadeux (Added for remaster)
Bloody Teddy Bear - Secret Weapon (Added for remaster)
A long convoluted secret allowing access to a secret area and weapon. (Added for remaster)

These are the obvious ones, there may be more

wow thank you. That's a lot that was missing :) Cool Nightdive.

New game plus? I'm definitely getting it now.

A bit late here, but previously censored models from the original release have also been restored:
some severed limbs, skinned corpses, and mutilated victims in the NY level, and two naked (dead) women in Jack's home.
That stuff certainly adds to the game's gritty and gloomy feeling. Not sure if there was more.

Very interesting... How do you know that this is included now?

I've played the game and seen comparisons. Even Tim Haywood (composer and audio director) confirmed these changes on Discord.

ok thanks for the information. I hope that part 2 will come sometime

Not so much cut but still good, in the original if you edited the game you could unlock the dev menu, in it there was a level called test level, trying to boot it would crash the game, in the remaster they figured out what the map was and re created it, it's nothing special it's just a U shaped room, what purpose it had is still unknown but the fact they even took the time to add it shows the care gone into the remaster, to see it in game open the console (press the key left of the 1 key below ESC) and type testlevelload 24 it's something 20 just keep trying.

Well they started adding content from the NV10 build, it was a build of the original game that would add more details in the world but they lost the code, so the story goes but years later someone found it and uploaded it, but it takes knowledge of coding to even open it, like i say they started but just stopped the biggest change is the front of the Asylum details like the faces on the wall and the Shadowman statues, i think funding for the game just stopped because even now my version says public beta, i guess they had big plans.