This movie just squanders its potential even though it has an interesting premise. The animation is serviceable but certainly not on par with sao progressive, mugen train or even the recent my hero academia movies.
Rimuru did not really have anything interesting to do and the powers that he acquired in season 2 wasn’t shown that much because the villain was weak af. If u like this series u probably will watch it regardless of this review and u might have fun but ultimately my expectation for a non canon movie is that it atleast can provide cool moments and good fan service(fight scenes,powers,etc) and this movie did not provide enough of that.