Please note that this review contains some spoilers, for both Steins;Gate 0 and the original Steins;Gate.
Steins;Gate 0 takes place after an alternate version of Episode 23 of the original, where instead of slapping Okabe, Mayuri begs for Okabe to stop trying because of how miserable he is after his failed attempt at saving Makise Kurisu. This goes through the events that eventually loop back around to Mayuri and Okabe convincing their past selves to go through with the original plan to save Kurisu.
I found that Zero ended up being very similar to the original Steins;Gate, in that the first half or so was more or less "good" and didn't have a lot of particularly impactful scenes, but the latter half ends up being fantastic and completely tugs at every emotional string.
Kagari was originally a character I disliked and found annoying and useless, however in the latter half she quickly became, in my mind, a very interesting and complete character that I only wish would have been given a little more backstory. I also originally didn't care that much for Maho, she almost felt like just a random character meant to fill the void of Kurisu and to become the target of "CUTE LOLI AWWW" jokes throughout the show, but she actually turned into a very great and well written character in the end.
Notes about the individual ratings:
Story - 9:
Turned out to be much better than I originally thought, I thoroughly enjoyed the story on my re-watch, especially the second half, even if I did notice some minor problems and thought a couple of things could have been done better.
Art - 7:
Steins;Gate never had that stellar or consistent animation, however it was noticeably better and more consistent in Zero. I especially notice that the tendency for character's heads to be off-model was resolved with Zero.
Sound - 8:
They re-use a lot of the same background music and sound effects, but they're memorable and great either way. I've always loved the Steins;Gate soundtrack so I was perfectly happy getting to listen to it again.
Character - 9:
I ended up absolutely loving every single major character and many character interactions. There were several partnerships and alliances I never thought would happen, and seeing certain characters stay good and not back-stab Okabe or the others was excellent.
Enjoyment - 10:
It's more Steins;Gate, my favorite anime of all time, and thus I enjoyed Zero on the second watch through completely and fully.
Overall - 9.0/10
Massively improved upon completion and dubbing of the series.
