(Please note, My reviews are completely opinion-based. In other words, just from MY experience from the respective website.)
To sum it up in a nutshell, It's horrible. I was a member for three years, I had multiple accounts during that time span. However I have been trolled, I have been betrayed, and all the time I spent there was a waste. I use to serve for the sonic fan characters fan club before I was IP banned for having a opinion that wasn't what the majority of the club thought... And the funny thing is, I have slaved away trying to make the club better. However my work was in vain. Most friends that I had there during that time eventually stabbed me in the back, so I almost couldn't trust anyone. There were some good people there that were reported off and is pretty much in the same boat that I am in. But I suppose it's a good thing to get away from that dump. When even Wikipedia refused to acknowledge a site, you know it contains fail. Fanpop should be avoided at all costs, it's nothing more then a sinking ship. Just let it hit rock bottom, it will do us all some good.
I won't go into full details, However the security is rather poor, the admins and mods are filthy liars(They allow a cyber-bully to remove my friend's accounts and pretty much worship him like a bobble-head.) The ad space is HORRIBLE, and it's generally unpleasant. I won't lie, back in the day... fanpop was half decent, but all the changes lead it to disaster.
Fanpop is pretty much in internet hell, any lower and if would encounter the likes of 4chan. It's best just to dodge this bullet, plenty of better websites exist. 1/5