We've been FIRE for almost four full years. The ACA was far better in the first two of those than in the last, for obvious political reasons well documented elsewhere. To the specifics you asked about:
* Re: "we could qualify for the subsidy by controlling income, which is discussed in great detail on other posts." Yes, do this whenever you can. It has worked out well for us.
* If you plan to work at all, as many FIRE types do, your monthly premiums are tax deductible. You can do that and qualify for the subsidy. Just something to consider if you have not already.
* Have you had to change doctors? No, we did not have to, but we did last month (at the 3.5 year FIRE mark) because we switched to Kaiser in CA to save $400/month on premiums. We are very glad we did.
* Is it hard to get appointments? No, it was not any harder than usual/before FIRE.
* Is it hard to get seen by a specialist? No, no harder than usual (the referral game, all that nonsense). It is MUCH easier with Kaiser, I'll say that much.
* Are some drugs not covered? It varied according to plan, but was no different than our pre FIRE plan.
* Bronze vs Silver vs Gold? We do a Bronze HDHP with HSA for additional tax savings purposes. We have used the HSA for co-pays and other things.
* Any good or bad surprises?
The bad surprise was a couple of doctors who saw the state exchange logo on our insurance card and looked at us like we were scum of the earth and the card might bite them as they dropped it on the counter and said "Ooooh, we don't take THIS Blue Cross insurance." Before you go to any doctor, call ahead and make sure they take not just the insurer name but your exact plan. Also, the doctors listed as in-network on the insurer websites are often not, in actuality, so I advise calling the doctor about that too. In many cases for us, the insurance was wrong, and we would have had to pay out of network. Also, doctors in the same office can be in-or-out-of-network. (I have family in the EU and have no words for how much I despise this inefficient, crazy, labor-making system in the US, but anyway.)
The good surprise is how much better Kaiser has been, for $400 less per month and the same deductible. So far, so good. Good luck!