Value object simple example and base class. Base class comes from @vkhorikov (https://github.com/vkhorikov/DddInAction/tree/master/DddInPractice.Logic/Common)

DateTimeRange.cs

using System;

class DateTimeRange : ValueObject<DateTimeRange>
{
    public DateTime Start { get; }
    public DateTime End { get; }

    public DateTimeRange(DateTime start, DateTime end)
    {
        Start = start;
        End = end;
    }

    public DateTimeRange(DateTime start, TimeSpan duration)
    {
        Start = start;
        End = start.Add(duration);
    }

    // Business logic
    public int DurationInMinutes()
    {
        return (End - Start).Minutes;
    }

    public bool Overlaps(DateTimeRange dateTimeRange)
    {
        return Start < dateTimeRange.End &&
            End > dateTimeRange.Start;
    }

    // Useful factory methods
    public static DateTimeRange CreateOneDayRange(DateTime day)
    {
        return new DateTimeRange(day, day.AddDays(1));
    }

    public static DateTimeRange CreateOneWeekRange(DateTime startDay)
    {
        return new DateTimeRange(startDay, startDay.AddDays(7));
    }

    // Equality comparison
    protected override bool EqualsCore(DateTimeRange other)
    {
        return Start == other.Start
                && End == other.End;
    }

    protected override int GetHashCodeCore()
    {
        var hashCode = Start.GetHashCode();
        hashCode = (hashCode * 397) ^ End.GetHashCode();
        return hashCode;
    } 
}

ValueObject.cs

public abstract class ValueObject<T>
    where T : ValueObject<T>
{
    public override bool Equals(object obj)
    {
        var valueObject = obj as T;

        if (ReferenceEquals(valueObject, null))
            return false;

        return EqualsCore(valueObject);
    }

    protected abstract bool EqualsCore(T other);

    public override int GetHashCode()
    {
        return GetHashCodeCore();
    }

    protected abstract int GetHashCodeCore();

    public static bool operator ==(ValueObject<T> a, ValueObject<T> b)
    {
        if (ReferenceEquals(a, null) && ReferenceEquals(b, null))
            return true;

        if (ReferenceEquals(a, null) || ReferenceEquals(b, null))
            return false;

        return a.Equals(b);
    }

    public static bool operator !=(ValueObject<T> a, ValueObject<T> b)
    {
        return !(a == b);
    }
}