Cost and abortion are the two biggest reasons for people to oppose the bill.
Right now the US is in it's largest deficit ever and people are leery of committing cash the nation doesn't have to an idea that is unsure. In the past, programs like medicare and medicaid have spiraled out of control as far as growing costs. That's my biggest concern about the bill, timing. If we were in a period of economic growth and prosperity most people would gladly support the bill. Since we are not, people are worried and scared about the economic future. And rightly so.
Then there's the abortion thing. It was the major issue in the House, which was surprising. People don't want abortion to be covered under the plan. But churches get tax exemptions so those people can fuck off. Personally I'm not for abortion, but I am pro-Choice.