The complaints have been many but the main grudge have been that NBC no longer broadcast many of the events live, unless you stream them online. In order to be able to do that you also have to have a paid cable/satellite/fiber subscription bundle expensive enough to include a bunch of NBC channels.
A large portion of these complaints can be ascribed to disappointment among people (like myself) who no longer pay for cable and would want everything to be free and preferably without commercial interruptions. But even if you discount those kind of complaints, I think the wave of frustration is a clear sign that NBC have totally misunderstood the role of broadcast TV vs. online streaming.
It is by now evident to most people that we are quickly moving towards a future where broadcast TV has a smaller and smaller role in our society, when more and more users cut the cord and move to online services as Netflix and Hulu for their TV/Movie needs. I think NBC saw this as well and tried their best to satisfy their users by putting the live content online (although with limitations).
Unfortunately NBC got things backwards, possibly because they do not understand what the future of TV looks like.
The main reason (there are others, like cost, fewer commercials etc) people use Hulu, Netflix, iTunes or other online resources (or even DVRs) is to give them control over when and where they watch the content. The ability to time-shift.
There is however one last bastion where broadcast TV still has a role (and probably will, for a long time), and that is live sports. NBC simply got things backwards, if they would have broadcasted the events live on their channels to the extent possible, and right after the live broadcast, made them available for viewing online, users would have been ecstatic! Especially if they would also have offered an online pass for say $20 for users who have already cut the cord.
I see a future where ESPN and other broadcasters team with Netflix or Hulu for making available sports events after they were initially broadcast. Today, this is a very underutilized aspect of sports content.