I'm not a Gundam fan, but my understanding is that "The Witch from Mercury" is very different from other Gundams. In particular, female main character + Yuri elements.
I know some people who are fans of Gundam who like Witch from Mercury. They tell me that its solidly in the Gundam universe, but its just so different its hard to recommend it to other long-running Gundam fans. In many respects, its something you need to think of as its own thing, despite being part of the mainline universe.
Its very much the Gundam writers going experimental and trying something new in their universe. Not all older fans agreed with the changes, they clearly were writing a story made for a newer audience and refresh the presentation of Gundam.
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Gundam is its own subculture almost distinct from Anime. There's "anime fans", but then there are "Gundam fans" who have their own thoughts / drama / discussions within there. When you have these long running series, it happens.
This is all fair. I do however like
TWfM because it isn't as deeply steeped in crippling depression as the rest of the franchise, and as such I think it makes a decent introduction to the wider
Gundam universe - especially for women, given that its leads are female.
As for the yuri, I mostly saw it as a massive step forward for big-name anime. Yuri in anime has almost always been either in non-mainstream series, or series that are yuri for yuri's sake, and such characters are very rarely the leads and very rarely depicted as anything more than stereotypical "lesbians are horny sexy fap material lol".
TWfM was, to me, two people in love with each other who just happen to be of the same sex, and it can't have been easy to convince a conservative Japanese media conglomerate like Bandai-Namco to agree to allow such a respected franchise as
Gundam to put a homosexual relationship front and centre. For that reason alone it deserves kudos for breaking new ground, in my books.
TWfM is certainly not the best or deepest
Gundam, but it has heart and its own identity.
Also true.