Another new feature although I would say syntax is Index Initializer. This features was although introduced in C# 3.0 and C# 6.0 provides just more concise syntax over that.

public class Class
    {
        //C# 3.0
        Dictionary<int, string> rollNumbers =  new Dictionary<int, string>
        {
            { 1, "Shakti" },
            { 2, "Rahul" },
            { 3, "Divya" }
        };

        //C# 6.0
        Dictionary<int, string> rollNumbersNew = new Dictionary<int, string>
        {
            [1] = "Shakti" ,
            [2] = "Rahul" ,
            [3] = "Divya"
        };
    }