Spongebob Squarepants is one of the rare shows on television that literally is fun for the whole family. Something all ages can enjoy, but I have to question whether or not its target audience (kids under 13) would understand all the references to surfing and the overall plot, which was a parody of 60's and 70's surfing tales.
The special was a let-down, offering nothing in the "quote" department, and very few laughs in general. Mr. Krabs was so badly written in this episode it was almost inconceivable, and Johnny Depp's hyped guest appearance was nothing short of awkward and forgettable.
Still, even the worst Spongebob has an appeal like perhaps no other cartoon ever has. That is why people will keep watching, and that is why more specials will come.