It’s damn funny and self aware
That’s almost all isekai today, though. Even the most hackneyed isekai authors are starting to realize the genre has been beaten to death so thoroughly that they must throws some new spin on their trite and the standard these days is “isekai but it’s self-aware!” Even that has been done countless times already.
I would agree otherwise as it’s excellent, but Re:Zero is definitely a harem. There’s a designated pairing from the get-go but it doesn’t stop the MC from collecting an army of girls that are all more or less infatuated with him.