i told them to get ps2 version of 2 and 3, but oh well.Playing 2 now.

so what is different?

There are a few differences.

There is less fog than the original.
The dialogue was changed in some parts, because small words were changed, nothing too big, but the subs are the old dialogue.
The streets are cleaner than the old ps2, and less obvious where to go at the start.
The game is also way darker.If you don't put brightness up you might miss something, and there is a good chance of missing something.I can barely see anything in the are to the flashlight, and i experienced a huge silent hill 2 hd bug on ps3.I opened my map around the are where you find the note on the door, and i went through walls of rooms with broken locks, but i think i fell under the world.I couldn't see anything with my flashlighton, and it was as if i was going under areas, because i tried to fix it by wandering around trying things, only to have to turn off the game without saving, so i lost very little progress, because i saved beforehand.

Ironicly you are safe in the silent hill underworld...

It was a glitch though.I am playing silent hill 3 now, which tries to feel like silent hill 1, and some areas do feel like it, but less scary so far than the first 2.