For better or for worse, Obama will always be linked to the Affordable Care Act. Heck, the colloquial reference for this act even bears his name, ObamaCare.
Undoubtedly, progressives will see this as a sterling legacy. Those on the Right will see it as his scarlet letter.
The same way that FDR is always remembered as the father of Social Security, so to will Obama be remembered for health care reform. The overriding difference, however, is that that FDR's legacy was always hedged by the fact that he was President during WW2. Whether you found his New Deal to be a blessing, or if you saw it as the dawn of the nanny state, FDR's leadership during the war made that thread moot and secured his positive legacy throughout the ages as an effective wartime leader.
Obama does not have such a display of powerful leadership upon which to hitch his legacy hopes. The same way that Lyndon Johnson's legacy consists solely of the Vietnam War debacle and the so called war on poverty, Obama will only be able to rely on the Affordable Care act and a vast series of broken promises, meekness and indecision in matters of foreign affairs.
In all probability, his legacy will consist solely of being the first black President. Everything else will always be the source for biased opinions from the left and the right.