Avantages
It is exciting the see the inner processes and infrastructure of huge company, the scale you see at AWS you will not see in many other places. There are opportunities for learning everywhere, although it might sometimes be difficult to take the time. The hiring bar is high and most of the colleagues are very smart people.
Inconvénients
Work life balance is not great. There is mandatory on-call (paid) for everybody, which plays into that even if the number of pages isn't that big. Not all products are all that interesting to work on. No matter what you will spend a big portion of your time working on infrastructure and less so on the product. This may not align well with the passions of frontend engineers. Promotion to senior level is notoriously difficult, many won't achieve it.