A passable episode, but not great.
In the time since Stamets became the nagivator thingy, they haven't yet touched upon the impact it's had on him or his partner, so it was a little odd to feature him here with still not a lot of exploration of that.
The groundhog day idea has been done endlessly in scifi, and while it's not an original concept at this point, I usually love this kind of thing because time travel. Unfortunately, it was not done particularly well here, very badly paced progression, skimming over more and more each time to cover up that it wouldn't have really worked due to the timing. It skimmed over it so fast that it actually appeared that Michael was retaining the information each loop, which was not the case. By the end they managed to get everyone on board very quickly before Mudd got to the bridge (which seemed to take him the whole time loop and yet he hadn't managed to really achieve much apparently). Skimming over it in montage didn't help. I also don't know how they improved their plan so dramatically for the final loop since Stamets had been taken by Mudd at that point, so not a lot should have changed. Maybe they skipped over even more loops in there. Even from the start they skipped over multiple loops. Poor writing and progression overall there.
Again Michael's character development was worked into the plot in a contrived way, with the whole dancing/kissing thing taking the forefront. On the plus side, at least the characters have stopped being assholes to each other, and almost feel like a functional crew now. Some of them are maybe even in danger of becoming likable.
I still can't accept this was Mudd. Sticking in Stella at the end felt so out of place and fan service-y, and only served to cement the disconnect between this and the character we saw in TOS.
-You're mad!
-No, i'm MUDD.
Writers, you've got to be kidding me.