CSI is still one of the top-rated shows on TV.

But even the President of CBS Entertainment admitted this week that the series suffered through a rocky season last year.

"It wasn't just about losing [William Petersen]. That show went through monumental changes last season," said Nina Tassler at the Television Critics Association press tour.

Those changes included the departures of series veterans Jorja Fox (who wil return this fall) and Gary Dourdan; and the arrival of Laurence Fishburne's Dr. Raymond Langston.

The drama tried to bring Langston into the team slowly. Big mistake.

"The challenge was to introduce [Fishburne] in a gradual way... so he earns a position of power," Tassler said. "[But] fans wanted to see him in a take-charge capacity."

That will take place this season for sure, the executive promised. She also said Langston would receive a makeover:

"Our research says fans love him and respect him, but that they just want to see him more comfortable in his clothes."

Among other changes, at least one other character will enjoy a different role: "Catherine is going to promote Nick [this season]," Tassler said, referring to George Eads' character.

CSI returns on September 24.

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.