How bad is it? Unfunny comedy.
Should you see it? Only if you're a completist for someone in the cast (which is unlikely).
Josh Mostel plays Howard F. Howard (yes, that's the level of humor), whose planned marriage to Melanie Chartoff is endangered by his growing obsession with the Three Stooges. He ends up on Stooge Row (Skidrow) - at the corner of Shaddup and Nyook Nyook - where people continuously relive their favorite Stooges bits. He gets sent to a rehab center, where he's treated by Sid Caesar in full-on fake German mode. It all ends in a pie fight. There's cameos by Victoria Jackson, James Avery and "Mousie" Garner (who you may remember from the Stooge shorts), plus a lot of archive footage of the Stooges, mostly from the Shemp era. Director Chuck Workman has an Oscar for his documentary work, but he just can't do comedy.
While on the subject, I'm not reviewing the few full-length Stooge films made at the end of their career: "Have Rocket Will Travel," "Snow White and the Three Stooges," "The Three Stooges in Orbit" and "The Three Stooges Go Around the World in a Daze" as they are all pitiful. Also, "The Three Stooges" (2012) is mediocre [I like Will Sasso as Curly] and I expect its upcoming sequel to be more of the same.