It's kind of ridiculous how well Resident Evil 4 has aged. I mean the original GameCube version was released in January 2005, which makes it 9+ years old, yet the game still holds its awesomeness, and not because of the graphic facelifts it's had along the way. The game just plays substantially better than RE5 and RE6, which in their defense were both solid games themselves, they just lacked the RE4 pacing and finesse.
In RE4 you follow Special Agent Leon S. Kennedy (introduced in RE2 as a rookie RC cop) as he heads to small European town to rescue the president's daughter from an evil cult. Unbeknownst to Leon, the cult is actually using an infection called Las Pragas to ‘indoctrinate' locals from the surrounding village, changing them into devout followers of the tweaked-out-verging-on-mutation kind… not unlike the zombies and mutations caused by the t-virus in previous RE games. It's all very over-the-top in that distinct Japanese/contagion sort of way, but that's precisely what fans of the franchise tend to relish. Honestly, the game's campaign is exactly the same as the five or six releases before the ultimate PC version, and as mentioned, it's still just as tense, thrilling, and action-oriented as it was 9 years ago.
As with all re-releases, there are those gamers that played the original, and those that have not. Unless you were a die-hard fan of the original, normally the re-hashes could be skipped because, as alluded to above, pan-generational games have a tendency to lose their luster across platforms, never quite as good as you remembered. Fortunately, RE4 is one of those games that still feels (and generally looks) like a contemporary masterpiece. It's a rare breed because it's not nostalgia but incredible gameplay that will keep you playing (whereas I'd argue that nostalgia is all that would keep you playing the remakes of the tank-control based RE games).
If you have yet to actually play RE4, the experience will be even sweeter with the Ultimate HD version for PC. This latest release has a few tricks under its belt to make it the “ultimate” RE4 incarnation – not only do you get a massive resolution bump from both the GC original (480p), and the HD (720p) re-releases on next gen consoles, but the Ultimate PC version also has high-def textures as well. And unlike the 30fps lock of the 360/PS3 HD versions, the Ultimate PC version can be locked at 60fps, making it the best looking version of the game so far. On top of that, it also comes with the extras packed into the re-releases that came before it. Specifically, the Ada Wong missions (“Separate Ways”) first introduced in the PS2 release.
That said, even now, almost 10 years later and being ported to PC for the second time, the game still falls victim to a few hiccups. I did notice a texture drop or two (ironic), and if you push the graphics/resolution too far, the slowdown could end up being horrendous. Because it's locked at 60fps, the next step down would be to 30, or worse, 15 fps if your system can't maintain the refresh rate (no inbetween). Granted this would only happen if you max everything out on the recommended hardware (GeForce 560), but at 1080 and certainly 720p you should be more than fine — though you forgo some of what makes the Ultimate Edition better than the HD versions.
That reminds me, for all the tweaking and enhancing Capcom have done to ensure the text, GUI, and graphics maintain their detail/readability when increased to PC resolutions, the game still only supports 16:9 screens. Black bars on the top and bottom personally don't bother me, but if you're going through the trouble to re-re-release a ~10 year old game to right the past wrongs of the original PC release (now seven years old), you may as well include all the bells and whistles.
In terms of control Capcom have finally hammered out kb+mouse input, and while the mouse makes headshots slightly easier, as the game progresses headshots don't necessarily bring down baddies. Also, you can still easily be over-encumbered by swarms of infected villagers, so the tension is always present. In spite of better kb+m compatibility, with full Xbox 360 Controller support I tended to play with the gamepad. Some keyboard buttons aren't customizable and sometimes it makes for a subpar experience (especially on the QTEs). Awkward keys, or worse, having to actually reposition your hand, kind of hinders the fluidity and intuitiveness that is present when using the fully supported 360 controller.
All of that said, if you haven't played it yet, the $20 that Capcom is asking for RE4 Ultimate is well worth it. It's at least 25-30 hours of what remains some of the best single-player action-horror gaming available. If you already own it on GC, PS2, PS3, X360 and/or PC, you may want to wait until the eventual 50-75% off next holiday sale, but in either case, it's a game you'll want in your Steam Library (even if you're double dipping). Afterall, this was a game so good that for many people it was the reason to own a GameCube.