The default Window control exposes an TaskbarItemInfo (https://msdn.microsoft.com/en-us/library/system.windows.window.taskbariteminfo%28v=vs.110%29.aspx?f=255&MSPPError=-2147217396) which is useful for manipulating the taskbar item of the Window instance.

There should be an easy method to add/override the shadow of a RadWindow. Either via XAML attributes or code behind.

<telerik:RadWindow x:Class="MyRadWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
        Header="Settings" WindowStartupLocation="CenterOwner" SizeToContent="True" ResizeMode="NoResize" MinWidth="500" MaxWidth="900"    DropShadowOverride="True" DropShadowOverrideBlurRadius="10" DropShadowOverrideDirection"-90", DropShadowOverrideDepth="3" DropShadowOverrideColor="White">
     
    <Grid>
 
    <!-- UI code -->
 
    </Grid>
 
</telerik:RadWindow>

When creating themed applications using RadControls, the standard Windows MessageBox control looks out of place.  With that in mind, the predefined RadWindows (Alert and Confirm) seem to be natural replacements for a typical MessageBox.  

However, when these dialogs open, they are silent  That is, they don't play any error, warning, or question sounds like the standard MessageBox - which makes them seem "strange" when used as a replacement.

Adding sounds to (for instance) the Alert window is fairly simple and can be accomplished like this:

RadWindow.Alert(new DialogParameters()
{
    Content = new System.Windows.Controls.TextBlock {
        Text = ex.Message, Width = 250, TextWrapping = TextWrapping.Wrap },
    Header = "Update Error",
    Opened = (alertDialog, eventArgs) => System.Media.SystemSounds.Exclamation.Play()
});

Though, it'd be nice if the ability to play a sound was built-in.  I'd suggest that the DialogParameters class used to customize the predefined dialogs be extended to support a SystemSound member of type System.Media.SystemSounds which, if defined, would play the specified sound when the dialog opens.

Provide out of box text wrapping in predefined dialogs.

All Windows messageboxes from Win95 have this possibility. 
Telerik in 2018 does not have this possibility, except through additional templates and additional code. 

Why to buy 

Make it possible to add "No" button to the predefined RadWindow.Confirm dialog without the need of custom Template.

To resolve this remove the MinWidth setting. You can set it back when the window is restored.

private double myMinWidth;
private void Window_WindowStateChanged(object sender, System.EventArgs e)
{
            var window = (RadWindow)sender;
            if (window.WindowState == WindowState.Minimized)
            {
                this.myMinWidth = window.MinWidth;
                window.MinWidth = 0;
            }
            else
            {
                window.MinWidth = this.myMinWidth;
            }
}

This is WPF only and not applicable for Silverlight.

As a user of the RadWindow control I want to be able to close it only by setting the DialogResult property without calling the Close method so that I can use it easily in MVVM scenarious.

As a <role> I want <ability> so that <benefit>.

Property for example.