Love the show, so it's sad to see that the movie didn't do any justice for it.
The beginning was strong and showed the characters well (although it seemed like the start of a filler), but the movie soon took a stumbling fall as the story progressed.
Having copy and paste characters were annoying and didn't add much to the story, nor were helpful in the final battle until the very end. The battle was far too quick and easy, due to weak, ripoff villains who, most of which, weren't memorable. It was also infuriating to watch Meliodas not outright say he wasn't Solaad (he did say multiple times he wasn't the dad's son, but never said he wasn't Solaad specifically) and then everyone finds out and is cool with it! Meliodas, as they all find out, is a demon and pretended to be Solaad and almost did a sacred ritual that he had no place in doing.
I don't want to dive too much into the topic of Hawk's mum, as this review is already pretty lengthy, but having her be a massive key part to the movie and barely having any screentime was not a good choice. Not to mention the fact that it had been shoved down our throats from the beginning that the Great Oshiro would be a key part in defeating the demons, although it felt like a side quest and a silly belief more than anything.
All in all, the movie really let down the show.