Well for one LA won't say from this premise that it isn't intense or anything, if not all the episodes from 1 to 11 are ALL episodic character episodes, be it gaining new members and developing the new characters or are "themed" episodes with no overarching plotline.
The "themed" episodes does feel like filler and yes it is, however the themes Musaigen no Phantom World gives does connect to the "Phantom" or weird occurrence within that episode, as for the character development, LA will say that the character development does help the characters from being stereotypes and being more well-rounded and defined characters and yes it's even from the filler themed episodes they get development through metaphors of the themes at hand.
LA's favourite character is being Haruhiko's first recruit being Reina Izumi voiced by ''Saori Hayami'' as her development and dynamic in the cast helped it get lively (unfortunately once she "enters and finishes her episode development she just becomes another love interest for Haruhiko) and come on Saori Hayami is voicing her, on speaking of Haruhiko, our bland male protagonist is nothing but a spouting expostionary character which can get annoying, he does get some character development episodes to his name and although not as powerful as Mai, Reina, Koito or Kurumi, subverts one of this anime genre tropes of "being too OP for his own good", he's still a dense main male protagonist though. Mai Kawakami is the reluctant fanservice girl of the series and LA gets why some people really like her, however LA still preferred Reina over Mai, as for Mai's development, LA saw that Mai got the best development out of the "supposed harem". The loner Koito Minase voiced by ''Maaya Uchida'' later on, the bear themed Kurumi Kumakura voiced by ''Misaki Kuno'' does get their own character development episodes but again like Reina falls under the harem and "joining the cast", finally we have Ruru voiced by ''Azusa Tadokoro'', the mascot of this anime series and is a Phantom who "helps" and LA says helps as loosely as possible the group, she's really just tags along than anything else until her one episode focused entirely on her. LA has been going to the basics of the characters for this review merely because the bulk of the anime is ABOUT the character interactions with each other under the "themed" or "character-driven" episode.
Oddly enough when LA said that this anime would have the cliched tired trope of "supernatural battle harem", it seems as if that's more of a "place setting" than the core focus of the anime, the core focus is developing the cast through themed episodes as well as building the world and lore of Phantoms and dealing with in wacky and hilarious ways.
In terms of animation done by Kyoto Animation, well LA won't lie, their visual flair and character designs are eye candy to see and with the "wacky" Phantom battles are sometimes a visual spectacle, even if it is a "supernatural battle harem", Kyoto Ani doesn't slack, and that's one of the finer points of Musaigen no Phantom World.
The ending comes in as a 2 episode arc and although the build up is rather predictable, it really starts getting good by the finale episode where that loose plotline way early from anime finally gets brought up as well as a small plot twist that actually made the finale well worth the wait to watch.
Musaigen no Phantom World may fall under the "supernatural battle harem" cliches however due to it's focused episodic format where they develop both the main cast but the world and lore of where Phantoms and humans interact with each other it's more of a slice of life battle harem with both huge expositionary moments from Haruhiko and some of it's anime genre tropes flipped for better or worse...but mainly for the better.
