Pining for Half-Life 2: Episode 3 is so passe. I'm more interested in Episode 4, which was being developed by Arkane until it was killed for being too good for this world. Or, for sensible reasons as revealed by Valve's Marc Laidlaw three years ago. It was to return players to Ravenholm, hence the name 'Return to Ravenholm', and some legit-looking screenshots seemed to bear that out.
I'm not just bringing this up to open old wounds—some new screenshots have been unearthed courtesy of those scamps at ValveTime. There are 11 of the beggars, purportedly taken from the portfolio of one Robert Wilinski, a Senior Environment Artist who was at Arkane between 2007 and 2008. You've already seen one above, but here are a few extra of the more interesting ones. (Having said that, they're all a bit boring—damned sewer levels.) Click this link, or watch the following video, for the others.
There are also a couple of images reportedly of Arkane's similarly cancelled The Crossing. It wasn't Half-Life related, but at least it wasn't set in a bloody sewer.