Take many of these exaggerative reviews with a big grain of salt. The animation is perfectly fine. It's a cartoon on CARTOON NETWORK. I don't know why people seemed to be expecting some Disney-level production.
That said though, it's unfortunately a bit of a bland show. It suffers from typical anime cliches like painfully slow plot progression and an unnecessary amount of melodramatic monologuing and brooding.
The plot is pretty simple and it's very obvious what's going on from the first episode, but the show still insists on wasting half the season pretending things aren't exactly as simple as they seem and it just kind of feels like its wasting your time.
There are just too many great shows on these days to keep giving time to something this unexceptional.