This is one show where I think while it has a lot of flaws and some weak episodes, its overall so enjoyable that it doesn't really matter much. There a lot of crazy plot twists and Lelouch is extremely charismatic making it easy to sympathize his actions. He is still the most popular anime character on this site after all. The show does have pitfalls like the parts taking place in the school which weren't usually needed and the fanservice can sometimes get in the way. It's also very over the top and sometimes the writing is poor so a lot of events don't make sense if you think too much about them. I think the first season is overall stronger than R2 and so enjoyable I gave it a 10 even though it's not exactly a "masterpiece".

How come the entire plot of this OVA is driven by some character's fanfiction?

I think the biggest selling point of this show is that has mass appeal. It has something almost all anime fans will enjoy and doesn't have more polarizing elements a lot of other really popular shows have. I think that combined with nostalgia bias helped keep it at the top of the rankings. I personally think the only real big flaws were the beginning was a bit weak because they expected you have to watched the 2003 version and the humor not being that funny.

I hate that the series pointlessly uses realism in the title when it isn't discussed in the show at all. Realism is an interesting political theory that I thought the show would go deeper in to. It doesn't even cover the idea of making trade-offs when governing or really much of the challenges of governing at all.