From past experience, their support is good, but one significant thing I missed was type inference:

    // function signature
    getNumber(context: any, callback: (result: Number) => void);
    
    // calling that function
    // unfortunately, here the type of num is any
    // unless I specify it manually
    getNumber(..., (num) => { ... });

Visual Studio figured out the type on its own.

Not really. Their support for declaration merging is buggy which makes many .d.ts files unusable.