Not collaborative

Amazon being a massive company with tons of smart people at all levels is actually a huge negative. You might be a solid individual contributor, but so is absolutely everyone else (or at least they fake it enough to get by) - and you're all fighting for the same attention. It can be very hard to stand out, and you have to ensure your manager and your manager's manager know what value you bring at all times or you're toast. (You may still be toast regardless.) That means politics, backstabbing, and stack ranking do occur, despite claims to the contrary. People definitely look out for themselves and themselves alone here. It's NOT a collaborative environment. It's also very easy to get the sense that you are a highly expendable cog even if your contributions bring significant value to the company. Plan to fight for yourself hard here, and be prepared to not get much acknowledgment or praise. 

Since the average employee ends up lasting less than two years, you will not see most of that stock and you may need to repay some of that signing bonus (usually awarded over two years) if you leave or are pushed out. Most people work startup hours, so their net effective pay rate is really low.