There was a thread maybe a year ago now, I forgot the name of it, that mentioned it and showed gifs, and I purchased it around then. I watched it about January for the first time iirc, maybe February. Since then though I've watched it pretty consistently to stop frames and try to mimic some of the art, so I can improve my own art.
5 CM sounds fantastic, I think I will watch that one next.
Surprised you haven't seen 5 CM yet. It has some of the most beautiful/animation music I've seen (get the soundtrack, it's amazing). However, don't go into the movie expecting an emphasis on story. It's not abstract, but it's more focused on capturing "emotions/feelings". Shinkai is pretty obsessed with that.
I would say, Garden of Words was probably his most straight forward narrative. So if you are looking for a front to back narrative with pay off, it's kind of there, but not really? Just go into it for the beautiful art, and the emotion he's able to capture (it really will give you the feels). Shinaki generally is more concerned about capturing emotion/feeling than anything else. Journey to Agarth (or Children Who Chase Lost Voices) is his fantasy epic, that is an homage to Miyazaki. So that one is worth checking out too (even if it has some flaws), it's a beautiful story.
I personally think Garden of Words is his best work, but people seem to gravitate towards 5CM and Voices of A Distant Star.