Chances are that if this is the method someone is using, to underhandedly debase you by posting on a public forum, they are also up to no good. If they want changes they can go to someone who matters and present their issues- otherwise they are doing nothing but stirring up sh*t and you should just take their opinions as meaningless.
We can't be everything to everybody, and some people are only happy when it rains. But as long as you are doing your best and reaching the majority of your participants, you are doing what you are there to do.
I have had times when I have subbed for another instructor for a few weeks because that instructor goes away, takes training, is on mat leave, etc and to maintain consistency it is good to have one other person to instruct the classes for the duration. I understand that at first people are rather accustomed to their regular instructor and meet me with a very scrutinous eye. But my frame of mind is that, "I don't really care if you like my personality or delivery right off the bat. I am here to give you the workout you came for and send you home validated." Of course I don't state this to them verbatim, I do it by taking control of the class and getting right down to business in a no-nonsense, direct way.
Once we get through a class or a couple of them, most participants usually come around, since I let them come to me when they are ready. And when they see that I genuinely care about how they are exercising, using technique, and communicate with them on an ongoing basis throughout the class, they usually appreciate this and understand that their regular instructor just has another method of leading the class.
I have even had several times when the class has asked when their instructor is taking more time off and I am coming back.... 
Changing the shape of the world one class at a time.