Mundo dominated in the preseason, fell off around February.
Kassadin was fixed and freed up a ban slot.
Shyvana shifted between jungle and top over and over, but was never oppressive. She was simply one of the best ones up there. Renekton has never fallen in power, just other champions buffed above him. And he still returned in S5 and crushed worlds.
Ziggs, Gragas, Syndra, Talon, Akali. There were many.
The game was about damage doing damage and tanks tanking damage. Shyvana actually built Ravenous Hydra and other damaging items. Mundo would be really hard to kill, but didn't heavily chunk as he does now so easily. It was about sieging comps and whittling down opponents until an opportunity could be found to engage.
Now we have tanks doing huge damage, assassins performing better as tanks, universal builds until nerfed such as Devourer/Rageblade and IBG/Sunfire. Tanks simply engage whenever because of their huge tankiness. We have champions comboing items like Steraks and Maw for extreme tankiness, shields, and damage.
I really liked S4 when damage did damage and tanks tanked it. The biggest flaw of S4 really was release feral flare and the first couple of games you didn't ban Warwick and Yi.