This review may contain minor spoilers
Liz and the Blue Bird (リズと青い鳥) is a side story of Hibike! Euphonium, focusing on the characters Mizore and Nozomi in their third year. While not absolutely necessary, I would highly recommend viewing the first and second seasons of Hibike Euphonium before watching this movie (it's 24 episodes over 2 seasons, but it's worth it, really good anime) as the plot is sort of a continuation of season 2.
The art is rather unique, but nevertheless pretty. The colours in the scenes depicting the Liz book were brilliantly done. In terms of character, I do feel that certain characters could have gotten a little more screen time for more development - in particular Ririka (or Ririca). More development could have happened on her relationship with Mizore.
The sound was definitely the star of the movie. The concert band pieces were brilliantly executed - the oboe and flute solo had me fawning and gave me goosebumps.
I enjoyed this movie greatly - especially more so being a fan of the Hibike! series. A must-watch if you, like me, are a fan of the series. If you are not or have never watched it before, this might not be the best introduction to the series but is nevertheless a good watch.