>>2254132well
compared to the vn? it's practically garbage
if you haven't read the manga or the vn and therefore have nothing to compare it to, then it's kinda good. not amazing, but not bad either.
the anime cuts out so much stuff. which is kind of good since the vn has the tendency to go off on a tangent sometimes (the manga doesnt) but bad since it also cuts out scenes which develop the characters or the plot
as for your concerns, umineko isn't really meant to be horror. some scenes are creepy or unsettling (especially in the vn) but it doesn't really try to make you feel scared. as for the mystery, i'm not really sure, since just saying 'the mystery' is too vague... but the vn/manga does go beyond the anime, so naturally there's more murders, but... how "mystery" it is can be debated. it's hard to explain without spoiling. also, the vn/manga goes more in depth on the murders and there's more debate, so if that's what you meant, then yes, i would say there's more mystery.
