A lot of the hate seems to be based on the delusion this show is somehow keeping a totally serious reboot of teen titans from airing or that other "better shows were cancelled to make way for this one. Neither of which is true as it's mostly an issue of the dreaded syndication mark that gets so many western animation shows cancelled. With multiple American channels trying to fill 18-24 hours in a day with different cartoons providers tend to heavily favor as many different shows as they can rather than a smaller number of long running shows. Fans tend to misdirect their anger in these cases as they believe that it is a case of a network favoring the new over the old and believing that the new show tested better in "focus groups".

A western cartoon that makes it more that 3 seasons is unfortunately very rare, and since cartoon writers never really plan out story arcs with a concrete end in mind, it often leaves older fans put out as so many series end without a satisfactory conclusion.

On-topic: The new show is decent, but it's definitely going for something different compared to the old show and the tone seems to be trying to set itself apart while still trying to cash in on the nostalgia of the old show, which makes me question exactly who they wanted the target audience of this thing to be.