The director's cut is a downgrade
The biggest problem is that they cropped it down from 1.85:1 to 2.35:1, so even if the content changes had all been good, that alone would have ruined it. Rocky IV, like all of the Rocky movies, was originally framed for 1.85:1 and cropping it to 2.35:1 made the framing look bad/cramped.
Cropping isn't the right way to make a 2.35:1 movie in the first place. The right way to do it is to shoot the movie with an anamorphic lens which squeezes a 2.35:1 image onto a 1.375:1 frame of film, which is then projected with an anamorphic lens that "unsqueezes" it back to 2.35:1. This uses all of the available resolution in each 1.375:1 frame of film; no cropping is involved.
When a 1.85:1 shot-on-film movie (like all of the Rocky movies, and tons of others) is made, it's shot with a normal lens (spherical lens, i.e., non-anamorphic), so the picture starts out as 1.375:1 and it's cropped down to 1.85:1, so you've already lost some of the film's resolution at that point. To then go back and crop it again down to 2.35:1 just because 2.35:1 is particularly trendy these days, is asinine. It's bad enough when people like James Cameron do this right from the get-go (e.g., Terminator 2), but retroactively doing it to a movie that was originally framed for 1.85:1 is even worse, because not only are you throwing away about half the film's resolution, but you're also throwing away picture content that was meant to be seen, and making everything look cramped.
As for the content changes, most of them were pointless; just alternate takes that weren't better, just different; changes for the sake of changes. Some of them were badly edited, like when they cut off the end of Rocky's original sentence and jarringly cut to Apollo's response while Rocky's mouth was still moving (during the scene where they're watching a video of their second fight together).
Also, they deleted the scenes showing/referencing Drago taking steroids, which were important scenes because they were meant to explain his "freakish strength." Speaking of which, we don't even get a sense of how strong he's supposed to be, because they deleted the line that says, "A normal heavyweight averages 700 pounds of pressure per square inch," so when we see "1850 psi" come up on the screen after Drago punches the device, there's nothing to compare it to.
There were a couple of changes I liked, but not enough to make this version even come close to being better than the original. For example, Paulie's "No sparring?" line finally makes sense. That line always seemed so out-of-left-field to me in the original, i.e., what made Paulie think of sparring, and how did he even know at that point that there would be no sparring partners for Rocky there? The director's cut gives Paulie's line proper context. I also liked the added bit of dialogue from Drago during the final fight, "He fights like a beast. How's my eye?"
It was worth watching because it was interesting seeing alternate takes and deleted scenes for a movie that I've seen probably 100+ times since I first saw it when I was 12 (1987), but it's far from an improvement over the original and I doubt I'll ever watch it in its entirety again.