As for the characters, they're definitely making major changes, but not all in the direction of making their personalities or motivations darker. Less subtle, definitely, but that may be inevitable for a big fantasy show that doesn't have time to capture all the subtleties that Jordan did take time for - or if it did take the time, would need to cut even more of the plot than it already has. Greg talked about wanting more of a LotR feel, but the thing is, LotR has many hours to tell a much simpler plot with far fewer main characters - and even then, a lot of the good stuff ended up on the cutting floor and was only restored in the DVD versions (which I personally consider as the real movies, I'd suspect he agrees).