http://www.planetphillip.com/posts/prison-escape-working-title-half-life-2/My friend from Uni has been working on this small mini mod. It's only 2 maps but he said it lasts about 40 mins which is quite impressive. I tested an early build and loved the new idea. The gameplay is HL2 in sense but it has a neat new idea which makes the maps unique.
Worth trying out I'm sure when he releases it sometime.