It's not bad, it's just...not good.
I haven't watched every single precure entry, but I have watched at least 5 and let me tell you, Mahoutsukai is my absolute favorite and among the top league of my favorite anime of all time. So, I had some pretty high hopes for this when it was first announced. After I found out about the episode count though, I became cautious. Then I saw the PVs and legitimately became concerned.
Finally all the weeks have passed, I managed to completely avoid spoilers and so came into Mirai Days with a fresh and empty mind that had not been influenced by other opinions. I finally binged it...
Hisui sucks so bad oh my god she was so damn annoying. Legitimately what were they thinking giving Mirai and Liko another pseudo daughter that is actually more like a realistic child? There's just so many moments where Hi-chan is being such a shithead brat. It really didn't help that within the show they constantly compared her to Ha-chan, their first pseudo daughter who wasn't absolutely insufferable.
She gets a little bit better, like a tiny bit, but not enough to make me actually enjoy her existence.
The story is also just like...ok. I can't get too deep into it because every detail is pure spoilers. Uhh, the main villain was boring but at least not as annoying as Hi-chan.
If you enjoyed the main series it's better to stay away unless you very specifically want to see the short cute shipping moments between Mirai and Liko.