I'm a former Exxon (pre-Exxon Mobil) plant engineer but I'll give you my thoughts.
Your location and type of unit (chemical or refining) will be a big factor in what it will be like to work as an operator. You will definitely be working a rotating shift - probably 12 hr shifts with a nominal 7 day long change once per month. You will work outside in all kinds of weather. If something goes wrong, you could die. (This really bothers some people
- some people are so worried they can't function. That in itself makes it unsafe.)
Exxon is a great company but you definitely need to conform to their way of doing things. You will probably hear that there's a right way, a wrong way and the Exxon-Mobil way.
Back in my day, we interviewed 3 or 4 operator candidates for every real open position.