Movie just released a few hours ago, just got home from the theatre having watched this in IMAX and- wow, if you could see the smile on my face.
Yes, being a long-term fan and reader of the novels and a huge fan of the word-building and lore of this series, I had a blast seeing Neia, Shizu and all my favorite characters from these particular volumes brought to life. The sound design and voice-acting was even better than I had hoped for. Each spell cast feelt extremely impactful, and Shizu's lines consistently got a laugh out of me and the rest of the theatre I was in, for example.
However, I REALLY don't think this movie will bring in any new overlord fans. It gives a BRIEF super-condensed run-down of the general concept of the story at the beginning, so someone unfamiliar with the series COULD watch it without consuming anything beforehand, but I imagine that it'd leave them... confused and concerned. Honestly, I don't think they should've even put that in there- this really is a movie only for the people already into the series.
To explain, the movie plays off and delivers a lot of it's fun to viewers through circumstance and character relations in ways new watchers simply wouldn't have the background knowledge and previously-established intrigues in order to recieve said enjoyment, or even be fully-aware of the fun to be had. That all being said, I still have a few criticisms keeping it from a 10/10 even as a avid fan:
A negative aspect of the anime that unfortunately carried over was their habbit of leaving too much on the chopping room floor. Of particular irk was the exclusion of the fight between Ains and Buser, talks between Remedios' help party and Blue Rose, and the throne room scene. These scenes would've helped the pacing and would've likely helped those that didn't read it prior to follow along, plus they are very fun scenes in the novels.
Also, since this movie is the product of two volumes smashed together, it feels really long due to there being a good 'ending point' feeling halfway through, and then it just keeps going. It's for this and the previous reason that I really think they should've just done two movies and made it a two-parter with a cliffhanger. That being said, if it HAD to be both volumes across a 2-hour runtime, they did much better than I imagine most studios would've done with the assignment.
Overall, I had a lot of fun and thought that it was great. There's a lot of enjoyment to be had here, just, I do NOT expect a bunch of positivity for this movie as new-comes wouldn't enjoy it as much, there isn't as much fighting as one would expect, and I can easily see some of those cuts not going over well with the more fervent and hardcore side of the fanbase, but again, if you're a long-term fan like I who's read all the novels but are not so into it you own an Ains body-pillow of your own you'll definitely have lots of fun.
