I really really like the art on the cover.
However, there are a few things about it overall that I'm not to fond of.
I think the text describing the book really doesn't do it justice. Specifically, the last sentence in the second paragraph "Every revolt has failed miserably" just doesn't seem to fit. It seems badly worded, like the way I would say something if I couldn't come up with anything else (and I'm really bad at that kind of thing). Also, if you want to bring up the oppression of the Lord Ruler, it seems like there would be a more creative way to do it rather than mentioning the revolts.
The last paragraph isn't bad, but something about mentioning Allomancy bugs me. As a new reader, I would have no clue what that is. I don't think it helps or hurts the case. Simply saying master the powers of a Mistborn I think would be enough, since they at least know that's the name of the book.
The first part is good I think, though the two quick sentences in the larger font at the top really wouldn't affect me buying the book.
The only other issue I have with it is all the advertising on the book of the price. I understand their reason for releasing it in this way (from the other thread where this was talked about) but with the advertising so obvious on the cover, it gives me the impression of "Buy me because I'm cheap and we need to sell a lot of me" rather than "buy me because I'm an amazing book"
I guess in the end, that isn't such a bad thing, since once people read it, they would know the book is amazing, so if that style of cover contributes to more sales from that standpoint, then it works. Just personally, I would be much more tempted to buy a $4.99 book that had a normal cover, with an advertising display around it with that info, than I would be to buy a book where it's part of the cover.
That is all just my (often fairly uninformed) opinion. Keep in mind I'm just a reader, and don't have any real knowledge or experience in that kind of thing.