IMHO. My Villainess quest. "Jishou akuyaku reijiou na kon'yakusha no kansatsu kiroku"

Usually a heroine who discovers she's reborn as a villainess demonstrates one of the two reactions: she either desperately tries to avoid becoming evil, or ignores being called one and goes away to her domain or another country. 

So at first glance,  "An Observation Log of My Fiancee Who Calls Herself a Villainess" is different. She's bravely embracing her destiny to become a villainess. And splendidly fails. 

And it would be absolutely boring if not for the fact that the focus shifts from this plain clumsy-but-cute-because-she's-in-love girl to her prince.

He's not the first lonely-and-bored male character who gets attracted to the blunt girl who explicitly states her feelings. However, he's one of the few, if not the first one, to be followed in such proximity throughout the whole series. 

So yes, 'Observation Log' was kind of surprising. Not in a sence you'd expect, but still.

The rest, however, is nothing outstanding, so labeling this anime 'the best ever' (like some users did on MAL) seems to me something only a very inexperienced otaku would do.

P. S. The language and manner of speaking in this anime are not difficult to understand, but I wouldn't recommend it as a source to learn Japanese because of the genre. Beginners will have hard time understanding the choice of wording in every given situation.