If a ContentControl is placed inside the control and the ResizeMode is set to NoResize the SizeToContent doesn't take effect.

As a workaround all you need to do is set the ResizeMode to NoResize in the Loaded event of the ContentControl.

Currently the template of the dialogs should be customized:
http://www.telerik.com/community/code-library/wpf/window/how-to-modify-the-alert-dialog-icon.aspx

Available in the 2016 Q1 Release: Added an IconTemplate property that provides an easier way to change the predefined dialogs' exclamation/question mark images.

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.

This happens when RadWindowInteropHelper.AllowTransparency is set to False and RadWindow is implemented as UserControl. The Window need to be maximized firstly on the main screen and then on the secondary in order for issue to be reproduced.

The issue also affects the ToolWindow that RadDocking uses for its floating Pane. In order to reproduce the problem, the primary monitor needs to have its DPI higher than the secondary one.

Available in the 2015 Q3 Release.

Available with the R3 2016 SP1 release. 

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

This is WPF only and not applicable for Silverlight.

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 the Window is opening or resizing and Winforms controls are placed inside its content the content flickers.

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 

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;
            }
}