By the way, just for kicks, I tried this out on my old Sony HD CRT display. The game looks absolutely killer on that display. It can't fully resolve 720p (true of nearly every HDTV CRT), but it accepts and displays it. The resulting image is very clean and smooth while the lower quality assets are slightly obscured by the lower resolution. It's so much cleaner than the GC version on the same TV.
On my plasma, well, I still think it looks good enough, but you can definitely see its age (as expected). Unlike some of the other HD collections, RE4 was designed with a very realistic appearance to its environments. I feel it was one of the first games to attempt to deliver the kind of detail we've grown used to in Unreal Engine 3 games. It's very gritty and full of debris. As it was originally displayed in a very low resolution (sub 640x480), however, many of its limitations were hidden by the CRTs of that era.
Look at something like MGS2, for instance. That game uses very simple, clean shapes to form its environments. It doesn't attempt to render gritty details and, instead, focuses on very clean surfaces and post processing. It's basically Super Mario World (MGS2) to Donkey Kong Country (RE4) in terms of how they've aged.
I think a little extra post processing could really have helped RE4. Would have also been excellent if they ported it to MT Framework and enhanced the lighting. Still, as it is, the visuals are the best you can get without resorting to emulation (which isn't perfect).
I really dislike how reviews keep throwing around the word "upscaled", however. That implies that the rendering resolution is still very low and scaled to 720p. 1280x720 is the native rendering resolution of these games. There is no upscaling occurring here.