I have only watched bits of Gintama, the anime is hilarious and very good. That's why I am not starting it now, I am waiting for the second season to go halfway through etc. So that I can enjoy Gintama without breaks.
Don't worry Gintama won't bore you, especially if you have watched a lot of anime before because Gintama has a hell lot of parodies. Gintama is just like "Seitokai no Ichizon" and "Sayonara Zetsubou Sensei", both anime are really really good. But in my opinion one shouldn't watch them unless he has watched a lot of anime before, because both of them have do a great deal of parodies and display a lot of references. I also made the mistake of watching them early on in my anime life. It is okay if you watch Gintama first, but if you want to watch the two anime which I listed then you should have a lot of knowledge about various anime.
Gintama doesn't really contain fillers, it is a comedy anime and there is not a real solid-story like Naruto and Bleach.