resident evil 2 is the easiest of all the resident evils... difficulty goes from hardest to easiest. i have a habit of playing every game on the hardest difficulty otherwise it's no fun
resident evil (director's cut) little ammo, few backpack spaces, a zombie can kill you in 3 hits, AND your current status condition is not represented through your avatar. if you don't check your health you will assume you're always fine... when in turn you can actually be 1 hit from dead but running like you're in the fine condition. also if you think about it this way there are difficulties within the character choices too, like this.
training - easiest = jill
training - easier = chris
standard - medium = jill
standard - tough = chris
advanced - hard = jill
advanced - very hard = chris
jill gets barry to help her with everything, she has 8 bag spaces and she doesn't need keys to pick locks. she also gets the bazooka.
chris only gets himself with the exception of rebecca and the piano. she doesn't heal him or anything in the original so she serves as no advantage. he only gets 6 slots, so you have to make frequent trips to the chest. also you end up having to leave a lot of stuff behind because you just don't have room to pick up every herb. but i hear he can take more hits... even though a zombie can still 3 shot you.
another thing that makes re tougher is that you can't just pound them with shots. if a zombie is in the falling sequence (as in you've shot him enough times to drop him to the ground) you will often waste a bullet because the attack isn't registered... also you can't unload on them while they're getting up because the attacks won't register. basically most of your shots have to be made while they are coming towards you, with the exception of getting one off when it first hits the floor. also the voice acting is beyond the worst known to man, you'll find yourself antsy and impatient going through cutscenes perhaps making more mistakes? bahaha... and i think zombies move a bit faster, but that's subject to opinion.
resident evil 3 on easy they give you everything you'll need weapon wise through the entire game, but even then nemesis is still a nuisance. on hard i personally have to kill nemesis every encounter for the deagle, western custom and infinite bullet case so it's not easy when ammo is scarce in the beginning.
resident evil 2... only one part of this game may prove to be a challenge and that's mr. x in his final form since he's a lot of like the final battle with tyrant in re1.