Well I'll admit that I haven't laughed as much as I wish I had. While (so far) there were definitely stand out episodes where I've burst out laughing, most of them never really got more then chuckle out of me. This is probably because the references were going over my head and dialog based humor isn't really my thing. It's always the jokes that rely on comedic timing that get me the most and the episodes I consider to be funniest (Katsura's introduction episode, the panty thief episode and the ghost bug episode) utilize this the most.
Also I am very hyped (and a bit scared) about the serious arcs. In fact my main reason for starting this show was the critical acclaim the final two arcs of season 4 got.
Gintama uses every type of humor, from complex layered jokes to basic poop jokes... and they all land. But it is true that the majority of the humor is dialogue based, so you'll have to get used to that. There are a lot of visual gags and slapstick too though and the sheer absurdity this anime goes to is unbelievable.
Well I don't exactly remember which was the first serious arc(because I actually prefer humor over fighting), but the fights can get absolutely to levels of high budget Shounen anime. They do get more intense over time, so don't expect it to go all out right away. Just relax and coast along, because this is a long anime with a steady upwards curve. lol
