The game's start is beyond turbulent, not only are the first few chapters fairly weak, before you even get to them you have to first read a plethora of side manga and 1 VN (although all of these are fairly short).
However by the time you get to Second Eruption things start getting into a proper order, chapters start feeling like actual meaningful events instead of the more vapid and short nature of the earlier ones and characters start getting proper developments eventually culminating into some really powerful arcs. After watching the documentary the reason for this becomes perfectly clear as it lines up with when they decided they wanted to ramp up their storytelling and try to convey something proper.
Do be warned though they will throw A LOT of pseudoscience later on and while I'm not one that usually minds this too much, it ended up kind of making me roll my eyes a bit and distanced me from the narrative at times, but in the end the game always managed to pull through when it counted thanks to its strong emotional core.

As a gacha game it obviously comes bundled with a whole bunch of problems, the actual gacha machine in this one for once is ESPECIALLY cruel, abysmal rates and needing to roll not only for weapons but also for stigmata, however, after second eruption (again) the story chapters give you their own fully equipped units meaning you baaarely have to use your own outside of Ely Realm way later into the story.
The fact Kiana is an actual main character with proper developments, struggles and dynamics with others does WONDERS to raise my opinion of this compared to other gacha games, and on top of this, Honkai also bypasses another problem the genre has for me, where the barebones presentation can seriously butcher important moments, by having properly animated cutscenes at the end/climax of most chapters. Thus Spoke Apocalypse (😭) , Because of You and Everlasting Flames are easily some of the most memorable moments in the whole series.

The gameplay quality can vary quite a lot depending on which suit you are using, Bronya's earlier ones are uhhh... otherwise just use a controller if you are playing on pc and it should be fun enough as long as you don't expect anything too overly complex, the different minigames they throw at you every so often can be sort of annoying at first but I eventually grew into finding them more cute than anything, it's not like they are very hard or take too long and look they straight up had to make up a Drakengard-ish dragon riding minigame that gets used in 1 mission in chapter 17 and that's it, no other uses. It's so extra for no reason, I love it.

I still have to do part 1.5 and I don't know if I'll be playing part 2 because it doesn't seem like the sort of thing I'd enjoy all that much but I do not regret the 200(!)+ hrs and the whole month I ended up spending on this game. Great ride.