I haven't been able to play and that's annoying. Maybe someone here can help...
I don't currently have a DVD drive in my PC because I needed it for another machine. Figured I could just drop in the CD key into Origin and it'd go and download it. However, Origin doesn't seem to think this is a valid key. Do I need to install form disk for the key to work?
I'd no problem popping in a Key from G2Play (which G2P almost always supply from boxed retail versions AFAIK) and downloading it straight away.
To the best of my knowledge any EA key from any source, Digital/Retail etc, is supposed to be usable with Origin (With the exception that older pre 2009 games are a bit hit and miss and may require support assistance to add properly).
I'd say possible you were unlucky enough to get a key from a batch that wasn't uploaded to their authentication servers or something like that and are looking at a support ticket to resolve .
EDIT: Apparently this link will add games manually to Origin, according to this thread on the Bioware forums.