I know this review is probably pointless to most people, but I had a hard time finding info about the movie in detail when I was trying to decide whether to watch it or not after watching the first season so hopefully this will be of use to someone! Also, for full disclosure, this was written from the perspective of someone who has only watched the anime and has not (yet!) read the manga.
This movie recaps roughly the first half of the first season of Haikyuu.
[spoilers if you haven't seen season one] The movie covers two arcs: Hinata & Kageyama trying to get into the high school volleyball club and Karasuno's practice match with Nekoma. Most other arcs/sub-plots have been excluded or greatly cut down. [end spoilers]
Would I recommend this if:
[minor spoilers ahead, trying to keep it vague] a small scene between the Karasuno teammates halfway through the movie and a childhood flashback scene between some of the Nekoma teammates right before the credits. [end spoilers]
I thought both scenes were cute, especially the last one, but I can definitely understand that not everyone will want to commit the time for such small additions. If that includes you, then maybe you can come back to this movie far into the future when you want to scratch the Haikyuu itch, but don't want to commit to completely rewatching an entire season or the entire show.