Actually a number of people misunderstand the term "boring" when they talk about Novak. When I ask some friends of mine why claim Nole to be "boring", to my surprise the answer is He has no typical game, no specific playing style, no trade mark shot...
They say when Fed or Nad walk into the court, people know exactly what they're going to show: it's the beautiful all-court attacking tennis of Fed and the 1,000 moonballs to opponent's BH of Nad. However, they never how Nole will play before a match. Unpredictable, or in other words: no true color -> boring.
To me it's definitely not boring. Change/adjust/adapt is never boring.
For example, his playing style in Wimbledon 15 and USO 15 final is completely different. He played much more aggressive in Wim final, attack with no hesitation, exchange Forehand toe-to-toe with Fed. Meanwhile, we had a much more patient Nole in USO final, he stayed calm and kept going to Fed's backhand all the match.
It's very very interesting indeed.