Polarizing anime. The first season was overall good, but had long stretches where the plot lost its way and meandered, and a bit of an asspull finale. I can see why some people would be turned off, or think it's just mediocre.
The second season was one of the worst anime I have ever seen, and sours the whole. Do not watch that piece of shit. It's fanfiction-tier at best.
I have not yet seen the movie(s), though I heard they were okay.