I like how easy tensor flow makes it to build a simple neural network. You can have a model up and running in minutes, but tensorflow still provides advanced users with the ability to customize models a lot.

Good documentation, large support community

The ability to easily write code that scales up to multiple CPUs/GPUs. Since version 1.0, there are higher level modules that provide Keras-like functionalities (e.g. layers, metrics). Moreover, it is definitely production ready. The best thing, though, is the Tensorboard tool that can be used to debug the implemented algorithms.