There's a couple of things people who don't like it criticize. For one, the Christensen footage is from an early test for Revenge of the Sith, so he's just weirdly glowering at the camera because he wasn't thinking about this moment when it was filmed. That's also why it's just Hayden's head comped onto Sebastian Shaw's body.
Then there's obviously the question of ... why Hayden Christensen at all? The implication is that the "real" Anakin Skywalker died decades ago and was replaced by Darth Vader, which kind of runs counter to the idea that he was ultimately redeemed by his love for his son as presented in the original cut.
Then you've got the fact that it kind of makes the original trilogy nonsensical in standalone. If you come to Star Wars and watch 4-5-6 first, there's some random guy you don't know at the end. It forces you to watch at least 1-2 and probably 3 first, or do something wacky like the Machete order (4-5-2-3-6), just so that the ending makes sense.
If you haven't figured it out yet, I don't like it myself. But I don't care because I've got the Despecialized editions, so Maclunkey it up.
The 4K trilogy (4K77, 4K80 and 4K83) are original theatrical film scans by enthusiasts. Where Despecialized manually recreated the originals by using multiple sources to restore changed scenes, the scans are just that. The results are ultimately very similar.
The main advantage to Despecialized is that it uses the official 4K Blu-Rays as its source for anything that doesn't need restoring, so it's mostly a professional quality transfer, while the 4K trilogy were scanned and cleaned up by fans. The main disadvantage is obviously that Despecialized is not a "real" theatrical cut while 4K is.
Either will probably satisfy somebody who wants to watch the unmodified orig trig.