It's the same "old" story. They said he couldn't run, they said the Suns couldn't even make it to playoffs with him.
Here is briefly what changed after Shaq has come to Phoenix:
He slightly (0.29 more points per 100 possessions) helps Suns' offense but the team has allowed 1.67 more points per 100 possessions. That points out worse defense since he has arrived.
The Suns are shooting with a better effective field goal percentage while opposing teams are also shooting better to Suns' rim.
This is what Shaq significantly changed. Better offensive (2.52% increase) and defensive (3.19% increase) rebounding percentage!
The Suns are getting to foul line more and also allowing opponents to take more free throws.
Turnovers per possession (1.7% more) are hurting! Opponent turnovers forced (-1.67%) has also decreased.