Well, Patrick Goldstein of the Los Angeles Times sure is, and he writes about it in this article:
-Yes, 150 minutes is very long for a comedy, but as someone who has read the script (and will have a review of the script coming soon), it only affirms that Apatow has been able to tell the story that he set out to tell, and if all turns out well, this will be by far his best film. Plenty could change from the script I read to the film we'll see in theaters, but if all remains the same, it should be something special.
-Time will tell, but what do you think? Can any comedy work at 2 and a half hours long?