To be clear, the insurance companies are still in charge, they are a monopoly market. The only thing that has changed is that they can’t deny you coverage. There is no competition among them, since they all turn to do the same things, raise your premiums, and make tons of profits.
If you think for a second that mandating people to buy health insurance without a public option was going to make any difference in the insurance market, then you were blind. What more couldn't make insurance companies happier, than to see people been mandated with no real choice for competition.
This cannot possibly be a government takeover when the so called free market insurance set the prices. As far as I know the only government intervention here is to prevent denying you coverage and making the insurance companies richer by mandating citizens to participate. More so, there is always room for improvement.