I can't judge, since I've only been a fan since SECRET. But I can say I personally didn't like the couple of months after NEXT LEVEL. More specifically after Rule/Sparkle, which I still loved. But then I didn't really like the album tracks and PV's on NEXT LEVEL. I also didn't love the singles leading up to Rock'n'Roll Circus, so I guess you could call that a "low point" for me.
But she completely and fully made up for it with Microphone and Don't Look Back, and I'm loving her 48th~49th~50th Single Anniversary thing so far, so I'm good now