I've been keeping an eye on the engine. Its C# support is progressing, but its not fully implemented. Once it's done, I'm sure they'll at least catch the attention of more of the Unity user base.
They use their own scripting language, GDScript (which itself is inspired by Python), but they also set up the engine in such a way that a custom language could be used instead.
One advantage of GDScript's implementation is that, unlike other scripting languages, there is no garbage collection--instead, objects are reference counted and automatically disposed of once that count hits zero. This helps prevent hiccups in the CPU because it doesn't have to execute memory sweeps. That said, it's still a dynamic scripting language, so mileage will vary and it's best to stick to good programming practices.
I personally think it's nice that Godot is pretty lightweight (not even 100 megabytes) and that you don't need an account or anything to just use the engine. It also has a dedicated mode for making 2D games as opposed to just slapping things together in a locked 3D view and calling it 2D. I don't foresee companies switching over to Godot given the financial investment in Unity, so it'll likely stay a mostly indie affair. That said, it was used for the Sonic Colors remaster.
They received an Epic Mega Grant several months ago and it allowed they to really push ahead with development, though from what I've heard, those funds are close to (if not already) depleted. Let's hope the momentum stays.