You really are not giving him a fair chance, i'd say.
I personally like Mistborn a lot, but can see why others wouldn't - please note it the second book he ever published, and while he started out as perhaps less then mediocre, there is a noticeable increase in quality as you read through his later books (compare Elantris to the Way of Kings for example and it is hard to believe they were written by the same author).
I understand many of his characters come off as generic in Mistborn, although I can assure you that if you read on in the series, the Lord Ruler becomes much more interesting, and less 'Dark Lord' ey.
Most of the peolpe who like the book, such as I, like it because of the imagination in the world and magic system, while being able to ignore the perhaps not so strong prose or characterisation.
Personally, I recommend you read Warbreaker. It's one of his later books - it's much more solid, despite a rather weak opening few chapters after the first, and you can read it for free on his website. His characterisation, prose, and all round writing in it are noticeably better then in Mistborn, and it also features an interesting magic system. Try it, and if you like it, maybe go back to some of his other works - if you don't, then you havn't lost anything.
I disagree with much of your assessment of the book, but if you dislike it, then thats your perogative. I do however think that Brandon Sanderson is a fantastic author (moreso now then he used to be) and I think he deserves another chance - particuarly as one of his more recent, higher quality works is up for free on his website (why it is, I don't know, but i'm not complaining).
Edited by Migey, 11 March 2012 - 05:17 PM.