For years, Republicans have been deriding the ACA (AKA: ObamaCare). They claim that it has been a disaster, that it needs to be repealed and replaced with a better program. This has been their campaign issue for years, and tRump picked it up and ran with it. Now that they have a chance to make good on their blather, they seem curiously unprepared.
When the ACA was originally being crafted and debated, there were a lot of compromises that needed to be made, due to the delicate majorities the Dems had in Congress (including Democratic senators from essentially red states), and the powerful insurance company lobbies. The biggest disappointment on the left was the lack of a "public option" (insurance provided by the government, such as the ability to "buy into" Medicare). The biggest aggravation on the right was the mandate. There was a lot of "fake news" being spread back in those days, so we created a site to combat that: http://www.healthcarereformmyths.org/
Nonetheless, it was successful for the most part. Millions of people were able to get insurance who couldn't before, the chances of having to go bankrupt because of medical problems dropped dramatically, and the overall cost for healthcare dropped. There have been outliers certainly, in particular those who are self-employed or run small businesses who don't get employer-provided insurance, and make too much money for medicaid assistance. They are a minority, and their problem could be addressed with a tweak to the law.