I've written about Mr Jordan's series often here, but I'll give you the Coles' notes version of it here

First of all, generally speaking his first 6 or so books are excellent. I'd put them up there with the first six books of SOT easily. However, like SOT there is steady a decline after that. The 9th and 10th books in particular are, by themselves, really quite poor for reasons I will explain further along. The 11th book picks it up again, and I havent had a chance to read the latest book though I hope to soon.
As a basic comparison of what makes each series good, SOT has a good overarching plot (Orden, Imperial Order) with excellent characters throughout. At times, like Pillars of Creation and Naked Empire, the plot of those specific books are not what they were for the rest of the series.
Wheel of Time, meanwhile, also has a decent overarching plot. However, the best aspect of the series is, in my mind, its 'mythology'. By that I mean, its magical system, the world Jordan has created with its history, its cultures, its creatures, and so on. Goodkind's mythology is good, but its not near on the epic scale that Jordan built. Jordan would rival Tolkien in his world building, but Tolkien is still in my mind the best in that regard since Jordan borrows some of the same concepts. Jordan's characters, meanwhile, are generally compelling but not nearly on the level as Goodkind's. Many of the characters are at times repetetive and downright annoying.
What really hurts the later books for Jordan is that he simply creates and follows too many story lines at once. I am not exaggerating when I say that in the 9th and 10th books he is following at least 4 or even 5 MAJOR plot lines, and within those plot lines maybe a few sub-plot lines each, and within those sub-plots a few POV’s each. So by themselves, books 9, 10 and 11 have almost nothing happening. Each major plot line gets its part of the book, and with all the POVs and sub plot lines you have maybe 4-5 chapters each. So nothing really of significance happens.
Now, if you group books 9 to 11 together as a single entity, you would have a compelling single-story narrative in that the span of those three books combined contains the main cycle of the major plot lines I mentioned above and all are building towards what is supposed to be the finale plot of the whole series: the Last Battle between the good guys and the Dark One. What makes the books more frustrating individually is that without there being any real plot advancement, or at least extremely SLOW advancement, all you have to make the books enjoyable are the characters. And like I said above, the characters have been around long enough by then that some of them have their tendencies exposed as annoying, uncreative and repetitive. You won’t really see it in the first half of the series, maybe because at that point there aren’t as many splits in the storylines and they’re still new, but you’ll sure see it by the 9th book.
All of this said, Wheel of Time is still one of my favourite fantasy series out there. I’d put it behind only Sword of Truth and then not by much.