The excesses of Rushdie’s imagination are both the strength and weakness of this novel.

The Shah of Blah

Haroun is more accessible than some of Rushdie’s other novels, which should make it a good starting point to learn about the author’s tone and style, both of which are in no short supply.  From the first page the whimsical setting is made obvious by the informal narration, fairytale quality of the story, and characters including Rashid who’s story-telling prowess is of mythic proportions.  
The adventurous plot develops into increasingly unreal dimensions that involve genies, UFO’s, and people who fight with their own shadows among other magical developments.  In less skilled hands or with a less humorous tone the story would read like an amalgamation of pulp stereotypes and fairytale nonsense, but Rushdie’s tone and comical characters can help convince all but the most serious reader that these story elements should be fun.
Just below the magical comic adventure, though, is a serious insight into the power that stories have in people’s lives, and how fundamental authorities—the kind that do not have a sense of humor to enjoy such a story—can wield power to harm people’s interior lives by depriving them of stories.  It is difficult to not read this underpinning in light of Rushdie’s own experiences of having a death sentence placed upon him because of his stories.

Khattam-Shud

One problem with the novel is pacing.  The first quarter of the book moves slowly and contains magical realism in the lives of Haroun and Rashid coming to terms with loss.  The rest of the novel, however, moves at breakneck through fantastical terrain, not giving the reader a chance to absorb the huge amount of alien information being thrown at them.  This shift into fantasy is not as abrupt as The Wizard of Oz, but neither is it as dramatic or carrying the same emotional weight.  
Aside from Haroun and Rashid, the other characters seem quirky but underdeveloped as they are rushed through the adventure.  Some, like Blabbermouth, get more time than others, but it is still difficult for a reader to know the motivation of minor characters and even more difficult to care.  Similarly, the struggle against the force antithetical to language and stories is familiar to anyone who knows The NeverEnding Story.  The magic of the adventure, then, will be lost to some readers who can predict the outcome long before the stage for the final conflict is set.

Ocean of Notions

It is obvious Rushdie had fun writing this story, and it is easy to have fun with him.  Doing so, however, means approaching the novel as though it were a popcorn action movie: suspend disbelief and indulge in the fun while it lasts.  The story otherwise becomes a forgettable piece of magic realism especially when measured against some of Rushdie’s other works.