Straw Hat Theater is made up of five shorts that aired alongside One Piece episodes 279 through 283 in October 2006. They are based on Oda Eiichiro's side comics that were drawn when he was given three sheets of blank paper by his editor and told to draw anything.
The first short is about Chopper Man infiltrating the lair of the evil Dr. Usodabada. The second short is a news report on what food was like for the Straw Hats before Sanji joined the crew. The third short investigates the hypothetical situation of "if the Straw Hat Pirates were Obahan, who would be the strongest?" The fourth short is about the bosses of the Luffione, Zorocia, and Sanjino families fighting for control. In the fifth short, all of the Straw Hats are carefree monsters.
Basically, these mini-specials were made purely for fun, and they are taken directly from mini-manga specials that Eiichiro Oda-Sensei himself made by animating them, and giving them life through the seiyuu, music, etc.
The stories are probably the weakest area of them, as every mini-special (save the 2nd one) is set in a alternate dimension using the Straw Hat Crew (other than poor Franky, as he wasn't a member during the time Oda-sensei made any of these...). All of the stories are crazy random, especially Obahan Time. But they the characters' follow along what's already established by them in the series, such as Sanji being a flirt and his rivalry with Zoro, Luffy liking meat, Nami's love for money, etc. Also, their names are different in everyone. XD
Retaining the style that Oda-sensei drew them in, they are animated with chibis, which I thought were adorable, granting it a 9 in the Art department. They're very colorful as well. :P
Sound gets a 10 from me, as it uses music from the series in it, and I love the music. The 2nd one, "Report Time," even uses one of my favorite tracks from my favorite One Piece Movie as the background music. It actually also has tracks I've never heard before in them, specifically Jingnai Time, and Chopperman. And he seiyuu's performance is amazing as always, (man, Chopper is so cute).
I have no choice but to laugh at them all. I actually just watched them before I typed this paragraph. Basically, if you watched One Piece and loved the antics of the Straw Hat crew there, then you absolutely have to watch these. Seriously.