Avantages
If you're a dedicated, hard worker, good at relationship building/maintaining, and perform well in the ranking this company will take you as far as you're willing to go. Your promotions will occur quickly and raises to follow. The career / professional development you will receive will set you up well for a long career within ExxonMobil or anywhere else. At the manufacturing level technical careers are not valued the same as management development, so many people feel pressured to stay on the management path to get out of the site to HQ before they express their true interest in other paths not related to management. Folks that are placed into high visibility roles early receive an abundance of guidance and support to ensure success which leads to quick development and promotions. The company tries very hard and effectively to gain great diversity in it's hiring classes. (For engineering in the Southern US I see more women and minority engineers than may other companies).
Inconvénients
If you're not in the top 20% of the ranking and more specifically the top ranked individuals after 5-10 years your career slows down very quickly as do the raises and promotions. The ranking system is not perfect and management perception can carry more weight than performance, even though management says that's not the case. Folks have been held back from promotions that are ranked at the top due to lack of visibility (visibility is position dependent and not due to lack of performance or capability, and can not easily be factor into the ranking system. Or a manager 1-2 levels above has no real direct experience with an individual yet discredits them for some small reason hurting raise/promotional opportunities). It is very hard to advance on a technical career path, and many technical folks become frustrated when their management development peers quickly accelerate through promotions and raises without much differentiation in ability or contribution. Work life balance is not encouraged or rewarded. It's considered normal to work 10-12 hour days. Many employees feel that this leads to folks who can stay at work that many hours regular get promoted faster. Folks who are not placed into high visibility roles can often be prioritized resources, development, and oversight from management leading to a sink or swim environment. Leading to a lack of visibility and resources to accomplish work which is then unfairly reflected in the rankings. With the great diversity every year of the incoming hiring classes, it's interesting to see a serious lack of diversity in the site management team (mostly white men, a few women, and slim to no minorities). No internal job postings. You're held responsible to drive career discussion with your supervisor. Then job moves are generally communicated to employees less than 2 weeks in advance, and if they aren't align with the employee's desires there's very little time time to work alternatives without a feeling of that potentially hurting your career.