the artwork is amazing. the story is great. the time travel is some of the best in media, there's only one plot hole throughout the entire story me and my friends noticed, and we like nitpicking a whole lot.
the characters don't appear very good at first but once you warm up to them you realize they're all pretty good.
the story sure takes its time to finally rev up but once it does it's just non-stop greatness.

but of course, it's complicated.
the story is certainly good but in the visual novel it's sometimes told in such a tedious way. the main character will repeat the same pieces of information to you over and over and over throughout the entire game, like you've been skipping through everything. you could probably read the very last chapter of this game and gather what most of the plot is from how much information the main character repeats. then occasionally, one of the other characters will sit there explaining a whole bunch of science stuff at you for like 10 minutes.
there's also a whole bunch of weird shit. i won't spoil anything but there's a certain character where half the scenes are just really fucking uncomfortable to watch, in a bad way. there are also a whole bunch of other weird scenes, but i don't want to spoil anything.

final verdict? give it a try. if you can handle the anime bullshit it'll probably end up as one of your favourites.