[chii]

> The engine is slow

doesn't really seem that slow for me (but of course, i haven't used it in anger yet).

> the editor is buggy, the language (GDScript) doesn't have the features of a modern scripting language.

the editor is enough for small scripts, but you can also choose to use your own native editor, or switch to the C# version (and use visual studio or jetbrain rider).

I don't find the scripting language any worse or better than any modern script languages. What are the missing features?

[sdkgames]

>I don't find the scripting language any worse or better than any modern script languages. What are the missing features?

lambdas, closures, support for error handling, constructor overloading, list comprehension, packing/unpacking (arguments/lists), varargs

[jokoon]

I guess most of these are syntax sugar or quality of life stuff.

Gdscript is a lightweight language, it wants to be fast. They explain the goal of the language in their doc and why they didn't use something else.