Gintama is an anime that makes fun of all anime, video games, and pop culture. It makes fun of everything, they rip of Dragon Ball, Bleach, Naruto, and a bunch of others to name a few.
If you have seen a fair amount you will get a lot of the jokes and enjoy it. I have seen all 172 episodes and still look forward to new ones coming out.
They even did an episode where they were making fun of the robots in Code Geass.