I don't really consider this to be "great IDE support", I consider this to be a start at IDE support. I love Rust, and I'm productive even without racer or YCM -- but I think there's a large gap between what Rust has and what many IDEs get you.

Most Java/C# IDEs will get you:

- Type-based autocomplete (racer/YCM/etc have this for Rust)

- Jump-to-definition / documentation (YCM/etc has this)

- Autoimport

- Non-grep-based refactoring

- Auto-boilerplating: for example, type `impl Trait for MyType` and have it tab-complete to a skeleton trait impl

- Some error integration (not just fileline jump-to), with tooltips and stuff asking you how you want the IDE to auto-fix the error

- A bunch of other smaller useful things which I can't remember at the moment

Now, autocomplete is a major chunk of this, but nowhere near being all of it.

The way I see it there are two camps on this issue. There's the "text editor" camp who use vim/emacs/sublime and when they are asking for IDE support they just mean autocomplete and jump-to that works from their editor. Then there's the camp coming from Eclipse or VS who want the whole deal.

The Rust Language Server project (https://github.com/jonathandturner/rls) is working on exposing this info from the compiler in a structured form so that IDEs and "text editor"s alike can get IDE features.