"Difficulty" is a bit of a tricky term to use when it comes to horror games, especially Resident Evil. The original game has very little in the way of execution challenges - the original release a bit more than the Director's Cut version, because you had to aim yourself. But honestly, I like Resident Evil more with auto-aim, because execution challenges aren't really the point of the game, in my opinion, and anyway the action in those games isn't particularly great, so it's better not to draw attention to it.
The original Resident Evil (especially the Director's Cut) is probably the least forgiving game in the series, though, for a couple of reasons. There's somewhat less ammo in the game than in any of the sequels, but beyond that, because the mansion segment that you start from is fairly open-ended, particularly with Jill, it's entirely possible to get into situations in the eary game where you'll be out of ammo; the last time I replayed it, I remember having to use the bazooka against normal zombies because I went for the western part of the Mansion first. Beyond that, the characters are way more fragile in this game than any game afterwards; Jill dies basically from two zombie bites, and the Hunters have that wonderful decapitation move. Of course, getting hurt is entirely avoidable if you play it safe, but you can only do that if you have the ammo, so you have to find all the hidden caches and know the right route to take, which isn't entirely obvious. If you end up doing riskier things - running past zombies, knifing and so on - the game really puts the hurt on. More than any other game in the series, Resident Evil makes you desperately want to find all the ammo you can and carefully calculate which risks to take to conserve it, which is what makes the game absorbing: it's not difficult, but it really makes you pay attention, if you see what I mean? In the sequels, running past zombies isn't such a big deal, because you can easily weather some damage - in the REmake, you have the defense items just for this purpose, Resident Evil 3 has the dodge maneuver, and in Code: Veronica (which, aside of its unfathomably stupid writing, is a pretty decent Resident Evil game), it takes like three or four zombie bites before you even notice it, and you're swimming in ammo anyway.
But, you know, I don't think that being difficult is inherently desirable for a horror game. The best of the classic survival horror games don't make you feel a challenge, they make you feel anxiety, gloom and the occasional bit of panic, and they achieve this by conditioning you to not want to fight by making combat inherently a drain on resources. The longer the player has successfully avoided death in a dangerous area, the more anxious he gets, because with every battle, his situation progressively gets worse and the further away he is from a dangerous area. A game in which you die a lot and start again from a checkpoint can't achieve that kind of sensation, because every time you die, you'll be back at a safe space, yeah? Resident Evil 4 is an action game, and sure enough, I remember dying a whole bunch of times trying out different strategies and weapons in different parts of the game. I'm pretty sure I died more in the game than I ever did in Silent Hill, or Dark Souls for that matter, but so what? Resident Evil 4 is a funhouse ride, death is not punishing at all, and the way the game showers you in ammo drops basically just teaches you to play with all of your fun toys instead of worrying about conserving stuff; I remember using grenades quite a bit, not because I needed them, but because I could really use the inventory space. An extended trip through the Otherworld in Silent Hill 1 is much less challenging, but it's also much more harrowing for it because you actually care about not dying.