Story - The story is often considered to be nearly non-existent in Gintama but that is mainly due to the constant flirtations with the past and main character development. When focusing on the present story it does indeed exist in the sense that what happens in each episode does impact later episodes to some extent (for the most part.) Like any anime/manga there are filler arcs, the only difference is that the quality of the filler is on par with the rest of the anime. Take note though, Gintama isn't all fun and games, there are several occasions where the story arcs are very serious, they rarely start this way and always switch back to the lightheartedness that is Gintama.
Art - There isn't much to say about the art, it is wonderful, and often has spikes of amazing. The art isn't particularly outstanding or extreme and could be considered rather plain but in my opinion it suits the anime better than some of the over detailed stuff that's out there. The backgrounds are well drawn and the characters for the most part are distinguishable by just their silhouette. Unlike a lot of comedic anime the extra characters often have noticeable features, and faces to boot.
Sound - Whether it's opening and ending themes or voice actors Gintama has made great choices left and right when it comes to sound. The background music always suits the mood and often sets the tone for what is about to happen. All of the voices match up quite well with their characters, that's not always a good thing but for the most part it's wonderful.
Characters - Minus Shinpachi this show is ten times above perfect when it comes to characters. Even minor characters in Gintama stand out well and were created excellently. Though as a rule there really isn't anything special about the supporting cast, their characters reach their goal every time, whether that goal be to give us a good laugh, or to give us goosebumps from awesome overflow they always succeed. Shinpachi isn't a failure of a character in fact he may be the most flawlessly designed, never betraying a single character trait, the only problem with Shinpachi is that he can be annoying as hell and has too much screen-time for such a bland person.
Enjoyment - This is by far the greatest attribute for Gintama, probably one of the most enjoyable animes of all time. Gintama's constant hilarity and breaking of the fourth wall make it almost interactive and draws you in immediately until it becomes difficult to stop watching. The ability to re-watch is one of Gintama's greatest assets, whether you're glued to your seat in awe, rolling on the floor laughing, or jumping out of your couch in excitement Gintama will always reel you into its pace and no matter how many times you watch you'll do the exact same thing. I've often found myself re-watching the entire series while waiting for the next episode to come out and laughing just as hard as the first time even though I knew the entire script.
oops I tried to make it concise at least.
