>>724172424
RE4 could be harder, even on professional with no upgrades the game is too easy to abuse, but it is still a great game though it takes some time to get used to it due to limited mobility.

Demon's Souls is pretty weird, the balance is all over the place, the combat is simplistic and there's grind for healing items if you're not good enough.
The story and characters are interesting enough and some controversial mechanics can make or break the game for you.

No idea about the other two.