Okay, it's, at first glance, obviously a Peter V. Brett book, but when you stick it next to the other three, it seriously jumps out in a bad way.
I haven't read the books (tried the sample of the first one, didn't like it) so I have no idea if there's a reason for the difference: if the first three completed an arc and The Skull Throne were starting a second series in the same world, I could see changing the design up a bit to make it look thematically similar while keeping the new series distinct, but I gather from reading the Tor post on the new cover that it's all part of the same series.
(The question is: will reprints of books 1-3 be redesigned versions that match book ?)
edit Looking at Amazon US, the Kindle covers appear to have the original cover designs--for books 1 and 2, it's the same art, but with the title much bigger and Brett's name much smaller. I expect the covers above are redesigns put out after it became a bestselling series and they wanted to capitalize on Brett's name.
Books 3 and 4 are showing as different than the above, but different in design from the original and the above designs of books 1 and 2.
Looking at Amazon UK, it appears that the above covers are actually the UK versions, and they have been redesigned with the new font (which makes it harder to read his name in the thumbnail!), although they can't quite seem to settle on a positioning and size for the book's title. Book 4 will still stick out, if it remains the same as above, as they've moved the novel's tag line down and moved the figure's head up.
In conclusion: guys, pick a design and stick with it!