Just read the book (29 September 2020)
I guess for someone not close to the reality of the Greek drama the past years and especially to the events of the 2014-2017 window, this movie can be a gentle introduction, depicting the general feel. For someone that was close to this small part of history this movie can range from incomplete to boring.
Personally, having read and enjoyed the book it's based on, I wasn't satisfied. Of course, it's difficult to move from 800 pages to max 180 minutes but still. I felt that important parts were not explained, as if it was rushed. I would much highly prefer if this would be a mini-series documentary rather than a movie.
Regarding practical issues, it's one of the first Greek movies that used music IMO correctly. Many of the Greek acting crew were bad (sorry), but regarding the protagonist he was spot on. I haven't watched a Gavras film before and I think I like him. There were some cheesy parts though, like the final dance thing but now, after some time has passed, I think these cheesy parts age well in your memory of the film. At the time though they were cringy as hell, but maybe my sense of the film as described above played a role to that feeling too.
Bottom line, if you are really interested in this era, just read the book. This movie isn't informative enough, it's just a film.