Anyone who thinks Whedon is the cats meow here needs to check up on history. When Dave Greenwalt was sharing duties with him their shows were successes both commercially, critically, and creatively. Whedon gets all the credit because it was his creation. But Greenwalt deserved almost as much or just as much credit as Joss did because after he left the shows lacked focus, drive, and purpose. When Joss was put in sole command of The Buffyverse things slowly turned to mediocre crap. Buffy Seasons 6 and 7 had almost more loss of veiwers per average then Heroes seasons 2 and 3. Yet no one was blasting Whedon the same way they blasted Tim Kring. Mostly because Kring doesn't have a leigion of Death Cultists dedicated to his praise and worship. And Kring sucks.
So Whedon by himself is not always a good thing. More often then not, it tends to be kind of bad. Look at Dollhouse. If Greenwalt was involved rather then Whedon I'd have more confidence in it. But neither are involved, so it will probably be just as forgetable as the first one was. That being said, it will still probably be more watchable then the last two seasons of Buffy and the last season of Angel. Because if Whedon was in charge of this thing, you could just ditch the title "Buffy" and rename it "The Spike Movie".