After 20 years of 3 amazing seasons with a decent 4th and 8 brain-dead marathons of creative waste, we get a celebration for the yellow sponge that embraces the worst traits this franchise has gained over the years thanks to Nickelodeon's habit of running the few good shows they have into the ground.
In this "Blowout Special", we get this rather bland plot that revolves around Spongebob & Patrick killing time by going on a land tour as his friends fight over on how to throw his surprise party. The closest things we get for conflict is Patrick's stupidity and the tour group being placed in an aquarium store. Also, the gimmick of Spongebob finding a human version of the Krusty Krab that has the voice actors playing them never really goes anywhere, it just feels like an extended skit among the other live-action scenes. The weak story would have been excusable if the humor and gags were entertaining but from the way this sentence is typed out, you can probably already tell that they weren't.
The comedy was beyond juvenile with the scene featuring Kel Mitchell dressed up as a giant bean that went around blasting people with a bean cannon being a prime example. The special, unfortunately, but expectedly, has an over-reliance on the nauseating and exaggerated animation style that had defined the last season or two of this show which results in the characters' mouths stretching across to the opposite side of the screen every other moment they talk. It seems that the writers have developed this mentality that if the animation is hyperactive, the show will be funny, but as Squidward learned with his marching band, being extreme only makes bad acts astronomically worse.
The only positives to this special are some neat callbacks to the series' history, especially the ones that acknowledge the Spongebob Movie, although, some of these references feel shoe-horned as the Tattle-Tale Strangler shows up to Spongebob's surprise party as if he were a friend and not some guy that tried to kill him. The last 3 minutes more or less gives us a competent "Happy Birthday" sequence that was actually enjoyable as there was a hint of some genuine emotion and a lack of emphasis on the squash n' stretch style.
To sum up, the only part of this special worth watching is the last few minutes along with the references and, to an extent, the "Trusty Slab" segment. It is not worth sitting through 50 minutes of a barrage of uninspired and obvious jokes just to hear everyone say "Happy Birthday Spongebob". I understand why they would make it an hour-long special. Nearly anybody would want a 20th anniversary to be grand and spectacular, but if the writing isn't good then refer back to the end of my third paragraph.