Ventajas
In 30 years I have never had a direct supervisor that I thought incompetent. While I have enjoyed some more than others, all of them were trying to make their piece of the business better. Some entry-level employees are difficult but they tend to not promote and attrit out the bottom.
Desventajas
It's easy to get into a pay band that doesn't include any physical peers, making it difficult to compare or see what your "competition" is like. Pay bands appear to be a little low and technical promotions slow. I've seen a lot of young people (I thought were "keepers") that left because they got impatient and could do better elsewhere. Being global, Shell struggles with multiple countries, cultures, languages. While they try to be respectful, there are a lot of things to miss and mis-understand.