People were butthurt over the rape stuff and how it came out of the blue. There is a jarring and massive tone shift after a relatively light opening involving the party that gets wrecked by the goblins before he shows up.
It's less visually graphic than the manga, but it's still really obvious what is going on.
That's partially CR's fault because they didn't label it properly, so a bunch of people got blindsided by it.
The anime itself is a decent enough adaption for what it is. If you like the manga, you'll probably enjoy it if you temper your expectations and don't mind things being a bit out of order and a not so great episode here and there.