I really don't know who should be the judge of what a good product is other than the people the product is intended for, them being "the masses".
"American Idol" is outlasting a lot of shows that I love, but remember, we're comic book nerds. Obviously, our tastes are different from the mainstream public and even different from each others.
JMS not being exclusive to Marvel is fine for me. For someone to choose not to be exclusive to a publishing company says a lot for their level of success, since he'll be without the benefits going exclusive offers. Any way, I hope I see him write some good stories elsewhere, while still freelancing for Marvel.
And I really enjoyed his run on Spider-Man. I didn't much like "Sins Past" nor the conclusion of the "Totem" storyline, but it was JMS on ASM that got me through high school.
The man's got my respect.