We'll see what happens, but I currently have a submitted enrollment.
1) The NY State of Health website has been functioning solidly for the most part, as compared to the federal site.
2) One caveat is that for those whose income can vary widely from year to year - like myself - it can take a few tries before gaining eligibility for enrollment.
3) Unfortunately, I wasn't able to retain my doctor or hospital of choice (LIJ) when I was under my ex-wife's plan. The majority of the quality hospitals only accept one or a few plans, and their premiums are substantially higher. It wouldn't have been that much more for me to stay with my doctor, but I weighed the cost and benefit and decided not to. I will be choosing a doctor in JH - random one rated decently on ZocDoc - and his affiliated hospital is Elmhurst. It's a substantial downgrade, but I am also relatively young, 100% healthy and good family history. I never use health care services except for an annual physical.
4) Overall, I would say that for those who need health insurance as an individual, ACA is a huge boon for NYC residents. Premiums were significantly higher for even the worse high-deductible plans out there, but they're manageable with the exchange ones. And of course, those under the FPL are eligible for subsidies and cost-sharing reduction.