I'll give it a B.
I got interested in Fourze when it was already in its 40th episode, marathoned the earlier ones in quick succession, then waited patiently for the rest. Despite the less time I spent in being invested in the show, I must say that the characters grew on me - the KRC especially, even Kengo, Miu and Shun, to a lesser degree. They are a fun group to see on screen as a whole - I can feel a semblance of friendship among them, even if there was little to no time devoted in exploring relationships outside of Gentarou/random KRC member (for example, Ryusei and Miu - with the former not really thinking the latter's worth her position as the president in the group but this was never really addressed/brought up again).
The Horoscopes were an interesting bunch of villains, and it was a nice touch that not all of them can actually be called a villain in the truest sense of the word. Their designs were also superb, and I think Virgo will be one of my favorite designs for a long time. I would have liked for another Horoscopes Teacher to have stepped in after Sonoda was defeated, but.
Like many others have already said, it's the pacing that jars the show for me at times. Fourze definitely took its slow time in building up the characters and their relationships with Gentarou during the initial episodes until Aries had been defeated, then came the Kyoto arc which was like a breather before the show plunged into trying to address the remaining plot points.
Gentarou's friendship plug sometimes is a bit too cheesy at times, but that's who he is and mad props for sticking with it until the end. All in all, I greatly enjoyed Fourze and despite its setbacks, and its characters would be the ones I'll remember very fondly.