The first time I watched erin 6 years ago I gave it a 10/10 but I just finished rewatching it and my score for it now is a 7 let me explain. I'd say this review is pretty much completely spoiler free so without further ado let's get on with it.
Story 7/10
I like the story but there is a LOT of recap and fluff throughout the series. I feel erin could benefit from being 40 maybe even 30 episodes instead of 50 and cutting out all the unnecessary parts of the show. I swear there are scenes you see over a dozen times in the show which accomplishes nothing but filling air time.
Art 7/10
I'm not really one for talking at length about art in anime but here we go. The art was fine. I love the artstyle of erin. Could do without the hideous cgi though.
Sound/music 7/10
The sound was also fine. I also enjoyed the music for erin as well. If I had to critique the music in any way first of all I swear the ost for erin is like 4 songs (with some additional songs just being sped up or slowed down versions of already existing songs) that play quite often which doesn't really work all too well when the anime is 50 episodes long. Also the second op (which is just the first op but sang by a different artist) is terrible... a much worse version compared to the original.
Characters 7/10
The characters for erin are quite solid and probably the strongest part of the show. My score might be higher if it wasn't for tweedle dumb and tweedle dumber... genuinely exclusively made the entire show much worse overall. If all the fart jokes were omitted that would do the show a favor as well.
Enjoyment 7/10
I'm not really sure what happened in the last 6 years that brought my overall enjoyment of this series from a 10 down to a 7 honestly. Probably just the sheer amount of anime I have consumed since my first viewing and the fact that I've just become more critical of anime over the years. I definitely still enjoyed I just found all the recapping and seeing the exact same scenes over and over again throughout the series to be far more off putting than my first viewing I suppose. I can't remember if I found the "comic relief characters" funny in the past but I certainly don't now and the fart jokes were embarrassing to watch rather than funny.
Overall 7/10
My overall sections tend to be my longest sections but I don't really feel I have much more to say about erin. As a drama it was alright. Plenty of dramatic things happened idk. I have to say erin is probably one of my favourite fantasy anime (and I don't really like fantasy so that's saying something). Erin is classified as a slice of life which I would say is accurate but still I feel the fantasy aspects of erin far outshine the slice of life elements. Well there you go. That's my review of erin. I felt like writing a review for this series since my score of a show has never changed this drastically before so I wanted to record my thoughts on the matter. If you've read this far have a great day.