The quality of the series remains pretty constant from start to finish, and there's not really any huge shift in tone or style later on.

As Legolas said, some parts drag a bit later on, but it's nothing terrible.

Personally, I much prefer Williams's near future SF with a few Fantasy elements like Otherland to anything he's done in pure Fantasy settings. I tried everything else he's done, because I enjoyed Otherland a great deal, but nothing else he's written so far as grabbed my interest nearly as much... or much at all to be honest.

His standalone Fantasy novel is fun to an extent, but I found MST terribly formulaic, derivative and boring and never got past the first book (even though I bought all the trilogy at once). Same for his more recent Fantasy series, I abandonned it after the first book.