Also once people start using GDExtension it should be easy to import languages to 4.x without recompiling.
It's a really impressive effort for an open source project. There's a channel on YouTube called KidsCanCode[3] (not just for kids!) which has a load of project-based tutorials to build lots of types of games.
[2] https://github.com/Geequlim/ECMAScript
[3] https://www.youtube.com/channel/UCNaPQ5uLX5iIEHUCLmfAgKg/pla...
I gave up on Game Maker years ago because I realized I was pouring hours and hours into learning a language I would never be able to use anywhere else, and as much as I like Godot (and I'm really starting to like it) I feel like I'm kind of making the same mistake. Even though Godot has support for C# and third party support for other languages[0..5] I have no idea how mature such projects are, or what the long term support prospects are.
Like as not, Godot is built for GDScript, most if not nearly all tutorials assume GDScript, and any plugins you find will probably be using GDScript. You can probably assume that GDScript support is guaranteed for the future, and at best, C# support is probably guaranteed for the forseeable future, though not necessarily at parity with GDScript, version to version.
Oh, and it also apparently Godot has its own shader language so forget about using GLSL as well, probably.
As far as the language itself goes, GDScript has significant whitespace, and I don't like significant whitespace. Its idioms tend to be just unfamiliar enough to me that I keep forgetting things that would be obvious in another language. I really wish it had lambdas.
BUT... it's still a capable language and obviously it does what it says on the tin. I guess you can stick with C# or wait until one of the other language projects matures, or just bite the bullet and use GDScript. The framework itself is so much easier to deal with than Unity IMHO, and for 2D I think it's worth the frustration. All of my issues with the language, thus far, are relatively minor and entirely subjective.
[0]https://github.com/perbone/luascript
[1]https://github.com/Geequlim/ECMAScript
[2]https://github.com/touilleMan/godot-python
[3]https://github.com/GodotNativeTools/godot-d