Just curious. Want to know your thoughts.
Solid Python support was the main thing that brought me to Panda, but the flexibility and wealth of important but not sexy features (e.g., pstats, task manager, BAM, TXO, PRC, etc.) is why I stayed.
I started working with P3D only recently after having spent a lot of time with the Blender Game Engine, and my main reasons for trying P3D were Python support, the free and non-restrictive user license and the engine still being actively worked on and supported. (i.e. opposite to abandoned or left entirely up to user-driven forks)
Python was mainly important to me because it’s the only language I’ve know well enough to use fluently, as well as the wealth and ease with which you can import external libraries and integrate them into a project.
As for the license, well, I suppose that speaks for itself, as does the “actively worked on and supported” part.
I still need to spend some time figuring a lot of features out, but I’ll join Moguri on the matter of “important but not sexy features” - the task manager being a particularly pleasant surprise when I discovered it existed.
Python’s support, open source, complete engine (i.e. it provides several subsystems: audio, physics, gui, …), deployment tools, profiler, comfortable pipeline for creating assets, wonderful community. Moreover, the engine is very flexible and well engineered. I feel comfortable with its compliance to Unix philosophy, since I prefer an engine focused on being an engine (even if I could see projects where other approaches might be helpful, but I am allocated on projects where Panda gives me the best tools). 
Its Python again. Our family starts our own game project and the girls shouted 3D over 2D. It might be a hard time learning all the stuff, but we are confident. Panda3D looks vital, interesting and it runs on Linux. So gaming on Linux written in Python led us here. 
Honestly for me it was 2008 and back then Unity and Unreal weren’t established as the industry standard as they are today. In fact in some aspects Panda was superior. There was Ogre and Irrlicht which had zero official scripting support and physics engine/GUI engine, etc included. There was something I think called gameMonkey but it used Java and even back then it was outdated for many people. Other similar engines such as Delta3D were simply inferior feature wise and others were limiting (genre specific, only 2d, only Windows, etc.).
Now its hard to find any reason in my opinion to use Panda over UE/Unity unless you absolutely can’t grasp C#/C++, absolutely need open source (uncommon OS, licensing fees), or have zero reason to learn a more powerful engine that you might use in a professional carrier later on.
Jut my opinion.