Although there are always hints of a larger overarching plot, I don't think the mangaka really cares, and after 90 episodes of sheer laughs, I don't care either. Gintama is primarily episodic but there are a few multi-episode story arcs. The story is secondary to the sheer joy of watching the great collection of characters and witty dialogue.
The art and sound too are secondary but by no means bad. It's no aural and visual masterpiece but it wasn't meant to be. The voice acting though is really good and brings the characters to life.
The selling point of this anime are the characters! A motley crew of caricatures, watching these characters interact is a joy in itself. The characters are constantly breaking the "fourth wall" in the sense that they know that they exist in an anime... brilliant! The dialogue is smart and very, very witty... sometimes bordering on the silly. This anime is not shy of laughing at itself!
There are subtle references to "Bleach", "Doreamon", "Naruto", "One Piece" and a whole bunch of other Jump publications, not to mention "Sin City", "Lethal Weapon", Chow Yun Fat and John Woo movies, and even "Casablanca"!
Along with GTO, this is one of the most enjoyable animes I've watched simply because I've enjoyed it, and not because I'm dying to find out what happens next.
I'll stop wasting your time now, stop reading and go watch an episode or two, you won't regret it.
