>>723968758 (OP)
>Are there even any reasons to go back to the original versions of the old Resident Evil games?
Yes:
They are vastly superior in every conceivable manner. They also pack near infinite replay value
>How different are they from the remakes?
Completely different games.
In case of DEmake 2-4, also completely different GENRES.
REmake 1 is the only okay remake of the bunch, and still the blueprint for how to do them right. However, it too relies on the assumption that the player has already beaten the classic RE1-3, and thus changes things a lot to challenge and surprise the veteran fans.