Mistborn was fun. I don't feel like I wasted my time reading them.
I've been on a break from reading any fantasy (or science fiction not written by Ursula K. Le Guin) and Mistborn was the first I've read in quite some time. I don't think Sanderson alleviated any of the issues that initially drove me away from fantasy, but I think it says something that I managed to finish three of his lengthy books despite that.
I like his world building. I like his magic system. I like that you're learning about history and culture along with the characters, and he knows how to make you excited about all the ~secrets~ and ~mysteries~.
He could use an editor. His plots are rather simple and I find the length of his novels unnecessary. He's not exactly a great stylist, but he's serviceable.
I heard that he was pretty good with female characters, but Mistborn was really bad in that aspect. Not as bad as other fantasy series, and yes, the main character is a woman, but she's kind of the only woman of importance in a very large cast. Which nowadays is a problem for me. I'm tired of tokenism.
I also have an issue with his ending, but I enjoyed the journey. So basically, if you want a long but light read in between other stuff, I say try it.