The Wheel of Time certainly is. As for the others I don't know. What I've heard of the Sword of Truth series is that after the first couple of books it gets very bad, very fast, and each book is apparently a repetition of the last, with more philosophy in it though. Raymond E Feist's just using many series, rather than one or two long series, but the effect's the same.
That said, there are lots of writers who continually produce quality novels - Steven Erikson, for one, who's writing a ten book series, and each one has improved upon the last (he's published 6 so far - I've only read the first 5 though). George RR Martin's another - his A Song of Ice and Fire is 7 books, of which 4 are published, and the first 3 are all amazing, and while the 4th took a long time to come out and wasn't quite as high quality as the last, it was still excellent and certainly not evidence of Martin just trying to milk his fans for more money (otherwise it wouldn't have taken 5 years to come out). R Scott Bakker has written an excellent trilogy with the Prince of Nothing- but we'll have to see if the quality begins to fall in the next one. Guy Gavriel Kay keeps writing excellent standalone novels
Outside of epic fantasy there are lots of authors writing continually excellent standalones - China Mieville, Jeff Vandermeer, Graham Joyce and some older writers continuing to write well such as Gene Wolfe and Michael Moorcock.
I don't know as much about science fiction, but I'd expect similar trends to fantasy. Either way, there are still hundreds of excellent briefer, older novels in both genres.