Ysera is such a situational 9 drop, either you are dropping her as a finisher on a won/nearly own game or you are hoping for to stall/Hail Mary a losing game. And the results in the latter case are a coin flip at best.
Cenarius, who I once thought to be mostly useless has really been pulling his weight. The 2/2 buff can turn the tide of a well matched game or regain control of a game that is slipping away. The two taunt option can buy you a turn and leave you a 5/8 drop.
I will agree there are better legendaries out there but I have come to realize he is not as bad as he may seem at face value. Give him a try and see if he works for you.
"You cannot defeat me, for I am the heart of the land!"