It's just a comedy, bro.
At its core, Gintama is a comedy that parodies pop culture, otaku culture, and the large library of Shonen Jump manga series. However, there is a coherent narrative behind the compilations of these parodies, introducing a unique storytelling experience that can make you laugh, cry, and smile (sometimes, all in one episode).
367 episodes, 2 movies, and an upcoming 2-part special and 1 movie later...
It's still a comedy. If you enjoy the first 3 episodes, then I'd suggest to strap on your seatbelts and continue on this rollercoaster of a show. This is a series that does not have the most well-planned nor articulate narrative, but it does a very good job of telling it in a (relatively) accessible package.