I am a fan and of course I would have liked Novak to have another year as good as 2011. But Novak's 2011 was one of the best seasons in the open era, so it would have been unrealistic to expect him to repeat it. But yes... I was unrealistic and I was expecting him to repeat it.
This year has not been bad at all: he hasn't lost to any player outside the top 10, he made the RG final for the first time, he won one grand slam and made the finals of 2 others and he's the leader of the race, with a good shot at ending the year as #1 for a second consecutive year.
There were some missed opportunities, and perhaps the most disappointing event was the Olympics, which was very important for him, but grass is not his best surface. Bad luck.
Taken in isolation (without comparing it to 2011), this year has been very good for Novak. As you say, the other three really fought back, as they were bound to do, and still Novak's won more points than anybody else in Grand Slams (5120 points) and also in Masters Events (4340 points).
If Novak manages to end the year as #1, 2012 will be an incredibly successful season, but even if he doesn't, ending the year as #2 cannot be considered as a bad season at all.
Having said that, I've been a Nole fan since 2005. I was happy with him being a one-slam wonder and the eternal #3. Everything else has been a bonus. I'm in heaven.