The major benefits of this law have been felt by consumers of health care. The law makes it easier for people to move from one job to another without losing health insurance as they move. It also ensures that the health insurance plan at the new job cannot refuse to pay for issues arising from a preexisting condition. In other words, if you have some health problem that has been ongoing, your new insurance has to cover you for it. This is a major improvement over the previous situation in which it was possible for insurers to deny coverage on the grounds that the condition existed before you came under their insurance plan.
The only real disadvantages are in the area of cost. By making insurers be more accomodating in their plans, the law makes insurance more expensive. The insurers know they will have to pay more than they previously would have paid and so they increase their prices accordingly.
Like everything, then, this is a trade-off. Consumers get better health insurance coverage, but the costs of the coverage rise.