Some people are getting screwed by the new system (very few) because they were in health groups that included mostly people without pre-existing conditions. Basically their pool was all healthy people, so premiums were low. Now they're finding out they can't just exclude all the sick people from their pool and their expense is going up. This is for the individual market only, of course.
So the result is that a few people are ending up losers in this new system. Now if we had moved to a single payer system, everyone would be getting treated the same way. The pool would be the entire United States (including fat people in the South), and we'd just pay a health tax. You may end up paying a lot more this way than you do now, but it would be hard to complain since it would be "fair."
I think the ACA may end up being better than a single payer if we can get past this whining stage. We still have private insurers who are motivated to keep people healthy and run things efficiently, etc, but we also are covering people who couldn't get insurance before.