Just got back from "One Piece Film: Red" and boy what a title. Saw it subbed because I don't hate myself nearly enough to sit through 2 hours of English dubbed One Piece. 2 hours, yeah, it was a bit much. It's kind of a sort of a musical, and the song sequences are probably the highlight, maybe? The singer girl has some real pipes on her, she really lets it rip a few times, almost sounded like it might hurt the old vocal cords.
Structurally, pretty weird. I'm trying to imagine someone trying to watch this just as a movie without any context, but why would anyone ever show up to a One Piece movie if they don't know One Piece? Normally OP movies are standalone affairs featuring original characters, and this has some of that, but what it really has is cameos from characters spanning the entire continuity of One Piece. Almost felt like the OP equivalent of Infinity War/Endgame.
Also, seems to be canon. Heavily retcons a previously mentioned world event involving a major character, so that was definitely something.
It was alright. Has the misfortune of showing up in the wake of Dragon Ball Super: Super Hero, and it doesn't hold a fucking candle to that one. And like I mentioned, if you're not an existing OP fan, you probably won't get much out of it, other than the music.