Taika Waititi's audio commentary for the home release of Thor: Ragnarok is absolutely hilarious and deserves to be heard by everyone who even remotely enjoyed the movie. He reveals a fair bit about his involvement in the movie on there too.
For a start, he reveals that while Clancy Brown did the voice work for Surtur, the mo-cap was performed by “one of the greatest actors in the world, not just New Zealand but the world, Taika Waititi.” He later also confirms that Korg is “played by Taika Waititi who is one of the great, great New Zealand actors.” Waititi also appears as one of the heads of the three-headed alien who escapes Sakaar.
On top of that, Waititi reveals that the Shake Weight that is part of Skurge's collection of "treasure" actually belongs to the director himself who bought it while in Atlanta filming Green Lantern. So that film wasn't ALL bad.
Slightly less factual is one of his other claims:
“I did all of the motion capture for [Chris Hemsworth] in the movie as well, so any time you see him walking around or talking that’s also me. I basically did all of the characters in the film.”