Oh My God I Love Zi-O. I have loved Zi-O from the beginning and I kept loving it all the way through. This was the show for me and I'm so glad. Rejoice, for with this we mark the end of the Heisei Generation of Kamen Riders.
Zi-O is, in my opinion, not that hard to understand, however it does require you follow the first rule of the .5 episodes; Don't ask unnecessary questions. As long as you do that, you're not going to get confused. Time travel is hard, multiple universes is hard, as long as you just accept this and take the little explanation, you'll be fine. Things are explained but a lot of people seemed to miss them, but if you pay attention it makes enough sense that if you don't think too hard about it it's fine.
Like everyone I think I'd of loved some more of the .5 episodes just because it was so good having the returning riders in it. I'm kind of just full of love for this series though.
Also the finale had such great references to Kuuga, and having Sougo accept the darkness within him in a contrast to Godai made a really nice bookend for the series. It gave me a soft spot, along with the similarities to Ryuki. It also felt like an actual end, where while I know these characters lives will go on, the actual story was over and a new one will begin.
Please watch Zi-O but ONLY if you have finished Blade and Kabuto because the show contains massive spoilers for both.
From my own collection...
List of Series
Lupinranger vs Patoranger