I worked at Amazon.
Amazon is a company with a strong corporate culture, but this culture does not reflect reality. They talk about "door desks" and like to think they are a startup- but the door desks actually cost them more than if they bought regular office furniture.
I can only speak of the areas where I worked, but none of the management, even at the lowest levels, was made up of engineers.
My boss had his degree in criminal justice! He originally wanted to be a prison guard, but someone somehow got him a job at Amazon. His mentality was that of a prison guard, and by the time I left, he had driven away %60 of the engineers in our team from mistreatment. His boss (she wasn't an engineer either) backed him up and it was that way all the way up the chain of command.
It is really hard to write software in an environment where the boss thinks all the employees are lazy, thinks that changing his mind all the time is ok, and that any delays this causes or complaints are insubordination.
In fact, it was not uncommon for him to tell us to work on some system that was not part of our area, because he didn't understand how the software was structured. We had a big chunk of responsibility, but more than once he chewed us out for bugs that were in code handled by other groups!
One of the other sayings is "B players hire C people, but A players hire A people". The hiring process is extremely arbitrary-- for instance the guy with a criminal justice degree was interviewing programmers and in order to get hired you had to get his thumbs up.
The offices were way overcrowded. Probably four times the density of any of the startups I worked for (and about 8 times the density of Microsoft). I worked in a hall, and I was lucky. It was noisy and a high interruption environment.
The pay is mediocre and they like to play games with your compensation, including promising things and then not delivering.
As others have pointed out, the code base is a mess. The company is in the habit of rushing off in some direction and then dropping the project. For instance, they used to have movie listings and restaurant menus on their site. They also used to (or maybe still do) have a search engine. So they force code changes across the ecommerce codebase to support these things, and then, once the feature is launched the team is moved onto something else. When I left the restaurant menus and mail order catalogs were several years old. This produces a lot of cruft.
As a result, they have a lot of engineers and a lot of engineer turnover. They have the same random changes in direction as any company. (I remember one thanksgiving we had to give up because Bezos changed his mind on thanksgiving eve about something we'd raised several weeks earlier and could have taken care of in plenty of time)... but since things are so poorly managed these changes in direction involve a lot of time and wasted effort.
They hire a lot of H1B people. Good people and I enjoyed working with them, but this was one of the sources of engineer turnover. The poor treatment and poor environment generally meant that engineering projects were slow and expensive.
This is why Amazon spends a lot on R&D. Not because they are really innovative. I think that probably %3 of their engineering effort is made up of really innovative engineers who are insulated enough to actually cut new ground. The rest of the workforce-- no matter how talented the engineers may be-- are hobbled by the code base and the extremely poor management structure.
No question it was the worst company I've ever worked for-- and I've had some intense painful startup experiences.
Amazon is a retailer that thinks it is an engineering company, led by people who don't know how, or don't care to, produce a good engineering environment.
They really care about fulfillment and customer service, but they don't really care about their engineers and have no clue about how to be innovative (generally).
But Bezos likes to go out and make pronouncements-- like a politician-- about how he cares about R&D and how critical engineering is, and all that kind of bunk.