I also watched it yesterday, but I didn't like it. And it wasn't the art style surprisingly, which I still hate, but that isn't what made me the most annoyed.
What made me annoyed was the music. Yeah it was great hearing the original song, but the songs during the movie... they just didn't match at all... when the pokemon were fighting... I didn't feel sadness I did during the original. It was the english version, so maybe the Japanese version was better, but the music was just bad.
I know they couldn't use 'Brother, Brother' again, but they could have at least used some of the sadder music from the pokemon anime. Like the original sad song they used after 'Brother, Brother'
I already don't like the original because it is not a great movie regardless what others say. But this made it worse.
One other thing that they left out, was Mewtwo blocked their special attacks, causing them to only slam into each other. If you didn't watch the original, they you wouldn't know why the pokemon didn't use their actual attacks.