Like in a recipe, Unfrosted has too many ingredients / seasonings that instead of tasting great, it became almost unpalatable as you watch and reach the end. There were so many sub-plots, too many characters and some scenes are just unfunny (like the living ravioli, the press conference with Kellogg's team of experts) & irreverent (the funeral of Schwinn - drenching a casket with milk & cereal? how is that funny?) . I adore Melissa McCarthy but sadly her portrayal of Donna "Stan" Stankowski failed to deliver, there's nothing funny about her, nothing memorable in her performance. One character that stood out for me is Harry Friendly, played by Peter Dinklage - he had just about 5 min screen time but his bit is the best part of the movie, IMO. Jerry Seinfeld must have been so excited putting together his project that as he kept building and building on his ideas, it became too much, and did not notice that the comic masterpiece he was trying to make has turned into a dud.
What I liked is the production / 60's vibe, and the end credits (with that catchy song and montage of bloopers, song and dance bits by the cast), it's actually funnier than the film itself.