Lopsided rarity spread even for literally whos, unjustified character shilling/power wanking, and rampant genderflipping aside, I definitely can agree that their criteria on servant qualifications can get really wonky. Things like allowing proper Divine Spirits to get summoned or the Marie case above, yeah. Oh and why did Onis qualifies as Heroic Spirits, again? Although with how literary characters qualify as HS too for some reasons, in the end I just really stop caring.
For the record not counting the crossover characters or both EMIYAs, the most recent HS so far is Mata Hari and Edison iirc (late 19th to early 20th century). Though personally, I think this is just Nasu softening his stance on HS qualification. I mean despite of everything it's still a project supervised by TM and Nasu in the end.
Mad Enhancement is pretty weird since idk, I think it feels like even TM writers forgot that the steroid itself can be turned on and off in F/SN.
/GO's strength is actually its writing tbh. Rome's awful and really padded with Nerowank and Orleans/London was p'boring, but the orders are mostly have solid writing at worst, while later Orders like Camelot and Babylon was pretty much among Nasu's best writing in my opinion. It's very story-heavy for a mobage (and is pretty much a proper VN by Babylon), and even the zany events (that are mostly barely canon jokes to fill time between order release for the players to have fun) are written competently in a way that's fun.
I'm not that much of a fan of the character writing angle usually used in /GO, although from what I saw it's something that people liked from it too. Some servants having stereotypical character archetype aside, just...I feel like they portray the servants overly positively. While Fate/ in general does that to portray the multiple sides of a figure, in /GO it just feels a lot more forced. The last servant I can recall that didn't get the dindu nuffin treatment was like, Medb.
Designs' hit or miss. Definitely gets better with time but hit or miss regardless. Though for literally bikini designs, swimsuit event servants aside I mainly recall Boudicca and Shuten. Liz Brave is from a joke event and is a walking reference for old bikini armor in DQ, Ushi doesn't even wear enough to count as bikini, Jeanne Lily's top might count, Mary Read wears school swimsuit and bunny ears for some goddamn reasons, and I think I forgot some others. Orite, Mordred 3rd ascension too, it makes barely any sense.
There's definitely good designs there too, and it's not really few.
Though yeah, despite its good sides I do feel that its main issues are mainly tied to the fact that it's a mobage that can't have as much character exploration as in other media (even if /GO does this far better than most Mobages already), and also have to constantly cater to whales and such by doing the things that it do.