Well, I just finished watching my 4K copy of The Matrix for the first time...and wow, it blew me away. I'd only seen one previous film on the format (the original Highlander), so I wasn't entirely sure what to expect.
Now, just one small detail - I do not remember seeing the film in theaters 25 years ago. I was old enough, but for some reason the premise of the film didn't appeal to me. I'd never heard of the directors, and of course Keanu was the only "fairly big name" attached. So even though I'd seen it several times on other formats, I was going in blind compared to the original version.
But now, after finishing it, I am truly speechless about what I saw. The various color tones were usually appropriate for the scenes they were set in, but keeping track of them all required some extra concentration. The Lady in Red was as radiant as a live-action Jessica Rabbit, while most scenes inside the Matrix itself were strongly saturated with yellow or green. The only real exception to this was the helicopter rescue sequence, where the colors sometimes shifted from shot to shot. For example, when Morpheus jumps out the window and Neo catches him, everything is very blue...but when Trinity escapes the falling chopper seconds later, the footage is notably brighter.
The only other color issue I noticed, is toward the end when Neo is trying to work his way through the crowd full of Agents. Just for a few shots, it seems Neo's hair is more gray than black, and then it goes back to normal. This could be something with the source, though.
I don't have a home theater sound system, but my room is so small I've never needed one, so everything played back fine in that regard. On the whole, a solid 4.5 of 5 - major props from WB!