I just binge-watched the whole series in a few days. It has one of the most compelling story arcs of any anime I've seen. The early episodes are interesting but not exceptionally so, with an unstable protagonist, a schlub, and some idiot cosplay girl. But it's amusing, and various characters are added. The time travel story starts slowly, but this is necessary, and the series becomes incredibly compelling as the results of small time shifts create big problems.
At times I got a little lost in the story, but the series does generally catch you up again, and while I would need to see some sort of elaborate diagram to see if this all holds together, in my mind it seems to.
The series is swimming in time paradox issues, and at times I think it's closer in spirit to fantasy than to sci fi, especially since there seems to be a rather unscientific concept of fate, but it's incredibly absorbing throughout, and the characters become surprising likable and nuanced as the series progresses.