sooo much asset reuse (to be expected), and in my opinion to many liberties.
For "thats what happened back then": we never saw the mini guardian, no one mentioned a time traveling mini guardian in botw, etc...
so either a non canon story, or
"the mini guardian only started to work when the calamity happened and moved from the prime timeline to this alternative timeline", so its a side story...parallel to the original BotW timeline.
Or "everybody got amnesia/brainwashed to only forget the small guardian"...
There is no consistens timeline variant where this is the story before BotW without either retconing BotW to hell and back, or this being an alternative timelien sprung into existence from the original.
And: the pictures they find on the guardian depict the castle during the calamity from far away...while he woke up during the event in the tower and transported right from there.... so how do these pictures exist? did zelda just stoped while they where fleeing and said "wait, let mi make a foto and send it to the shika cloud".....?
Gameplay: its a muso alright. Feels like hyrule wariors. First mission was fun, secend already became tedious to me. The framerate is something alright... Im not super fragile to framerates, but the stuttering in Links Awakening, and this... its getting hard to ignore it.
A no for me. As someone that played the original Hyrule warriors, and thinks that BotW is one of the best games ever... yeah, its a fanservice game, with a lot of loot and numbers, but not many decisions to make. popcorn game. Thats okay, if you are in the mood for it. I would rather have a good hack'n'slash (DMC, Bayonetta) or a game base around exploration (BotW).
For people that did not play HW or any musou game, there is no excuse not to try it.
The demo shows the gameplay really well.