Maybe it's just a sign of the increasing maturity of the free desktop. More likely I think it's evidence supporting the contention that GNOME's six-month release cycle has institutionalised a culture of conservatism. Either way, the release notes for GNOME 2.18 are distinctly underwhelming.
Every six months the list of new and improved features gets less impressive. Sudoku is a major new feature? I should be itching to upgrade so I can view PDFs in a slideshow mode? It almost makes me want to give the latest KDE a test drive. Okay, I'm exaggerating.