Thankfully, this game's modding community is huge...
The PC version is worth getting only if you're one of the most die-hard RE4 fans out there. I would NOT recommend getting it if you're playing it for the first time. Why? Because it's simply one of the most lazy ports of a game that I saw yet - it's actually worse than the originals. You won't enjoy it as much as if you got it on Wii, for example.
Gameplay. Nothing changed, here. It's the same exact thing as the other versions. The only twist is about the awkward controls. You'll be dammed if you don't happen to own any kind of PC gamepad - the game is almost unplayable with just a keyboard. And don't even think about using that mod which enables aiming with the mouse, it's even worse than a keyboard. If you have trouble playing games like Devil May Cry or GTA:San Andreas on PC, trust me, you'd better forget about Resident Evil 4.
Graphics. Here's the big letdown. Remember when everyone went crazy about the PS2 version's graphics? Well, take those exact same graphics and remove fog in every maps from the game. You may think it's not such of a big issue, but :
-You'll see every buildings/doors clip in and out as you move around. Not very nice for the eyes.
-Performance is hurt a lot because, when there's no fog, a lot more models and stuff are on-screen. You'll see as far as the eye can do, which makes the otherwise moody maps totally drab. Also, If I don't use any mod to add fog, I can't even get 30 FPS in certain maps because so much stuff is shown. And I got a quite decent rig (P4 3,2GHz, 2Gb of DDR2 RAM and GeForce 8400 GS)...
-No fog also means you'll see the enemies coming from very far distance, which terribly hurts atmosphere and gameplay.
The textures are also so blurry. The overall world almost feels like Nintendo 64 only with more polys and models onscreen. Yes, they're that bad.
Thankfully, there are countless mods out there to fix these problems. You can almost make this game look like an Xbox360 one with the appropriate mods - Bloom/HDR, Dynamic Lighting, HD textures... just make sure to have a good PC !
Sound. Well, it's the same sound effects all over again. There's only one difference : the gunshots sound effects dramatically changed into something that will -again- make you cry for mods.
Nothing much to say about the soundtrack though, other than it still rocks. It's just as good as it used to be - I still listen at it regularly on my PC.
Bottom line. By now, I think you might got the main idea. PC RE4 is just a lazy port which is playable (and enjoyable) only thanks to the modding scene. The mods are the only reason why I bothered dealing with these awkward controls..
Pros :
-RE4's core stays untouched - jumping down ledges, climbing ladders and contextual moves are still around..
-Great soundtrack which still manages to add tension to the atmosphere.
Cons:
-Game would totally suck if it wasn't for the mods.
-Horrible gun sound effects and graphics.
-Takes a way too good PC to have a decent framerate, considering how a simple PS2 can run this game flawlessly.
I give this game a 6/10