Well, I was bored by Gintama for 4 episodes but never as bad as with Sket Dance. It just didn't hook me enough from the get go but it wasn't sth I had to watch in parts either (as it was with SD). In other words it was an average anime which I could watch if I had nothing better to do. But after seeing 5th episode I started to like it (it was the one with Gin and others delivering a bomb to an embassy, the scene when they found out what was in the package was hilarious), mainly thanks to introduction of Katsura (my favourite character I like him even more than I like Gin). And
after seeing 8th episode I became a fan. There was the most hilarious fight and one of the most hilarious scenes I've ever seen in any anime/manga. And from then it got even better. The most important thing however was that characters were really great. All of them. They were perfectly designed and I liked them from the start. In SD I was annoyed by them from the start.
In short, even after seeing one episode only I can tell that Sket Dance is not anime/manga for me even though it's similar to Gintama. But the differences between them make a huge difference. I'm glad that author of SD has managed to achieve such success and that he has fans but IMO his inferiority to Sorachi is obvious.