Personally, I think Sweet did a decent job on some of the covers. Eye of the World was a nice cover, Dragon Reborn was epic looking when I first went to the store to buy it. I hated the painted cover of ACoS. I have the first print release of that one without the painting cover and have never replaced it.
Honestly, the more I think about it, the more I think that the Sweet covers are just kind of "blah" for me. A couple are epic, but for the most part the rest don't really do the series justice. I mean, they're pretty, but I want epic!
And the Great Hunt cover Sweet did, as I have mentioned before, is a disgusting travesty. I don't know what he saw when he was reading the book but that short little elf ****er had better not be Loial, or I really will do the peeing thing.