On Windows 8.1 in IE11 I get a blank screen.
If I switch the Document mode to 10 (F12 → Emulation), then Webplayer works.
I am getting the same issue with IE11 on Windows 7, with Unity 4.3.0f4 builds
I’d suggest submitting a bug report through the Unity editor.
You should be able to modfy the HTML to force the correct doc mode as well. there are several ways. Here is an
http://blogs.msdn.com/b/ie/archive/2010/03/02/how-ie8-determines-document-mode.aspx.
This metatag should do the trick