The engineering of Blender is super impressive. The code is held to a really really high standard for people to merge their branches into main Blender. Just look at the time it takes for it to open, and the space it uses.
While 3dsmax maya use many gigabytes and take a while to open, Blender opens instantly, and is only 200 megabytes with a full install. The PBR branch looks absolutely incredible, but the FBX interop is still a complete disaster. It would be great if UE4 had a importer that could read .blend files directly into the engine.