I've found just the opposite actually. While it's far from perfect, it has been amazing for rapidly standing up new apps (especially prototypes). We've used quite a few different strategies and found it to be flexible and performant.

The only downside is we do find ourselves sometimes implementing relational DB functionality at the application level to compensate for Dynamo DB's "flexibility." Postgres is still the go-to for data that is relational in nature. But man, letting Amazon worry about hosting and scaling is also pretty awesome...