What ruined the WWE? For me, it was the transition from 2013 to 2014.

1. From 2010 to 2013, WWE was full of interesting storylines and characters
You had the Nexus, Punk vs Cena feud, Cena vs Rock WrestleMania matches. The main event scene was Cena, Punk, occasionally The Rock, Sheamus, Big Show, Alberto del Rio. What happened after 2014? Cena became a midcarder with the US belt, Punk left, The Rock disappeared, Sheamus became a dork with rooster hair, Big Show was in the Authority (HORRIBLE STORYLINE), Alberto del Rio lost his entertaining rich guy gimmick. The Shield guys never clicked with me, and while the Wyatts were interesting at first, WWE had them lose every match.
Now what is there? There's no main event scene, Reigns and Lesnar are part timers, there's no full time main eventers.
2. The changing of the logo and the titantron, in fact, there's no titantron anymore, just a giant fucking screen and even the ramp and the ring have screens!!!
3. It's not shocking that after 2013, WWE began to have record low viewership and today Raw struggles to get 1,5 million viewers, in 2012 they were getting 4 million regularly and 5 million occasionally