Open source, rich echosystem of add-ons (KiCADstepUP for 3D, KiCost for programmatic BOM generation, RF layout tools, via stitching tools, autorouter...). Fast response by the developers themselves on the KiCAD forum. Very rapid development (CERN, the European Organization for Nuclear Research, which operates the world's largest atom smasher, adopted KiCAD in 2013). pcb is highly scriptable in Python. Active efforts to interface KiCAD to the open-source QUCS RF simulator, FreeCAD mcad, LTspice, and, to a lesser extend, open-source openEMS 3D electromagnetics simulator.
Lack of a UTF-8 compatible library manager (there is one which is not UTF-8 compatible). Lack of ODB++ support (this is a very closed standard, though). Padstack could be better (but this is expected to change in the upcoming version 6). The At the moment, file conversion only from Eagle is nearly flawless (but the file structure of closed-source software is closed, so it is not easy to write translators for them).