Evidently experiences differ extremely. Yes, some people report horrible experiences but in my case it was nothing of the sort. The oral surgeon gave me some tylenol for after but I didn't need it, pain wasn't an issue. The procedure itself was somewhat longer than most cavity work by my regular dentist, but nothing extreme. His office was across the street from my dentist. He told me that among his clients was the chancellor of the local university. He wasn't the cheapest. If and when I need another I'd probably go back to him. My problem was a cracked tooth that had dental work already. The crack(s) had allowed bacterial infection to reach the nerve. There was some question to begin with which tooth was the problem. I couldn't say, but he determined which it was, he had his methods of determining that. I wasn't in tremendous pain, but it wasn't comfortable, so I had it done. This had to be around 10 years ago.
i've had 2 root canals, the first was a complete screw up and the dentist left a burr from the tool and part of the root. two years later and an oral surgeon had to pull that tooth and replace it with a bridge.
the second root canal went swimmingly.
bad dentists suck.
This is no joke. I experienced some residual numbness (it was pretty slight but it wasn't going away) after a dental procedure by my usual dentist around a year ago. I called him a few days later and he was quite concerned. He talked to an oral surgeon that had an office in the same building and he called me back and told me he thought I should take a prescription steroid (pills) to facilitate healing the problem, and I did. The numbness went away after a few weeks. The particular procedure that he did was problematic, it was difficult to get good anesthesia and problems like the one I had can happen, not necessarily because he made any mistake.
I did some online research about lingering nerve issues after dental procedures and discovered that a lot of people have terrible aftermaths that last indefinitely, lingering, absolutely chronic pain problems that they find it extremely difficult to live with. Some of these problems never go away! Do a Google search on Lingual Nerve Injury and you should find some sobering horror stories. For instance here:
http://lingualnerveinjury.blogspot.com/. I wouldn't go to just any dentist.