Ventajas
The Shell brand is a well-recognised name. It is a very large organisation so it is easy to find a new job or a comfortable niche without ever leaving. There are plenty of places to shelter from economic winds of change. Benefits are very generous, especially if you stay there a long time - which is easy to do since job security is very high. There are opportunities for travel.
Desventajas
Many, many, far too many people "making pretend work" to justify themselves. There are many areas where people repeat the same tasks, passing small changes back and forth to each other endlessly to pass the time, but they do no constructive work. There is little or no performance-reward connection. There is huge inequity between people who have been employed at Shell for several years, and those employed more recently in terms of the pay levels, job security, and work conditions. There are a lot of "contractors" who have been working in the same office and role for up to 10 years but receive contractor pay rates because nobody is responsible for their budget. There are far too many "expatriates" employed with special treatment, but expatriation is used excessively - some "expatriate assignments" are between neighboring countries and others are concocted by people arranging (unnecessary) meetings for themselves in other offices. The focus of the "safety culture" is on rules not principles, so it is not effective and just creates excessive bureaucracy, particularly if you work in an office.