There's a lot to say about this edit. First and foremost, it was better than watching the original movie. There are also several moments of pure genius/fun. Did I enjoy it? Not really. It's still Justice League and it's still bloated and struggles to find a balanced tone, and it's still full of boring scenes I wanted to skip through. It's important to establish firmly that I think the DC movies are pretty horrendous overall, so I was biased going into this, but I wanted to have fun and enjoy it so I did my best.
Regarding the edits (keep in mind this is all subjective and I'm sure a lot of people would disagree with me):
The music edits sound like they're separate from the film, and often are too low in the mix. Some of the music is excellently placed (MORE Sabbath = Good Time, I also loved a lot of the canned background music during the more dialogue heavy scenes) and some of it is genuinely terrible (if I never hear the riff from Kashmir again in my life it'll be too soon. I could also do without the Johnny Cash- it's just so overdone. And the song playing in the last battle when Auquaman jumps into the air was just terrible terrible terrible). Some of the sound effects were pretty fun though. There's also a number of instances where original music bleeds in, but it's not the end of the world.
As for the video editing... it looks more to me like a bad CAM rip then an old film reel. I don't think the "Grindhouse" look is very successful on the whole, BUT there are a number of moments where it looks excellent (usually when there is heavy CG backdrops and/or bright exteriors). I also think a TON more could have been trimmed.
When this edit works it works well, but because it's still 2+hrs long the "Grindhouse" aspect starts to wear thin. Had it been a super cut of just awesome action scenes and tighter melodrama it would have been a lot of fun, but as is it struggles to find balance. That said, if you're a fan of Justice League you'll probably have a lot of fun with this edit.