There are other reviews, official and user, that scream about the amazing video and audio, special features, and how basically, you can get rid of your extended dvd copies of the films (and theatrical releases, if you have those, I guess. Why would you even have those?). I'm just here to address the concerns over the supposed flawed color correction in Fellowship.
First of all, I viewed the the films (DVD and Blu-Ray) on an LCD television, calibrated a few years ago using what is considered its ideal settings, taken from AVSForums. Nothing special beyond that, and those settings haven't changed since I first bought the television. I viewed Fellowship in its entirety on Blu-Ray, and then specific scenes that were known to be altered, between the DVD and Blu-Ray.
When watching Fellowship as a whole picture, and looking for anything odd in the picture, I must admit I noticed nothing. During the initial Hobbiton scenes, I noticed no green sky, no cyan grass, nothing like what was shown in the side-by-side comparison video that popped up not too long ago. Any changes that were made to the picture worked well enough that when viewed in context with the scenes before and after, worked perfectly. Even when trying to find anything that looked out of place, I was unable to do so (and keep in mind that having viewed the DVD of Fellowship many times, I had an idea in my head of how the film should have looked).
By the time I got to the infamous shot of the ring in the snow, and that entire scene, I had completely forgotten that I was supposed to be looking for color correction, and everything looked fine; nothing stood out to me. When I finally remembered that I was looking for color correction, I rewound to the beginning of that scene (The Ring goes south), and again watched for the color change. At this point, I did notice a difference, but there was no green sky, no green snow. If anything, there was a slight bluish sheen to the shot, but the snow was still white, and as with the Hobbiton scenes, the color grading fit so well in context to the shots before and after, that it fit perfectly in the scene, especially considering the emotional impact the scene was supposed to convey.
When comparing those specific scenes (and a few others) to the DVD version, there is a noticeable difference in the color. However, this is not a bad thing. As I understand it, Jackson and Lesnie changed the color grading in those scenes to make them fit better into the film as a whole, and this is accomplished. In fact, when watching The Ring goes south scene on the DVD after watching the Blu-Ray, the old color scheme created such a tonal shift for me that it made me squirm. The realism of the snow shots took me out of the fantastic world they were trying to create.
So, are the changes made noticeable? Only if you're doing a straight comparison of different versions of the film, which is pointless. Watching the scenes in context, not only are the color changes not really noticeable, they actually fit better than the original versions, just as Jackson and Lesnie intended. Those people who are complaining and saying that the color changes are horrible, or stick out like a sore thumb, are either EXTREMELY nitpicky, sore at having to buy another version of the films and complaining about anything except complete unaltered perfection (which come on, why would you have ever bought anything beyond the extended DVD's almost a decade ago?), or, having heard about the color changes, are looking for something that's not really there.
This version of the films are the definitive, comprehensive version, and can't get any better in terms of video, audio, or special features. Get rid of your previous versions, and enjoy. What we've been waiting for has finally arrived, and is as good as we've hoped.