I watched this anime Iast year, expecting to get a light story. I didn't know that I was about to meet a piece of jewelry.
It's hard to explain what Gintama is about. It can be describe as a comedy, shonen and slice of life. If you watch the first 50 episodes only, you will probable think this is a comedy. But you'll be wrong. It's much more than that.
It's not the classic shonen, our protagonist Gintoki, doesn't have (and need) power ups. He's lazy and dumb.
Character development is incredible. Don't expect to get one-dimensional characters, especially on Gintoki's side.
Gintama is very "similar" to life: It has funny moments, tragic moments. Funny and dumb people being serious, serious people being funny and dumb.