Genetically, in terms of the present day East-West affinities, the La Brana / Loschbour HG people, how intermediate they were, we can use projected samples from current world PCA to estimate this:

- from the supplement of the newest Lazaridis paper

- from Davidski's Eurogenes Project (
https://drive.google.com/file/d/0B9o3EY ... sp=sharing for a zoomble version)

- from an early draft from a paper reported by Dienekes in 2012.
There's some differences, but it seems like they are in line with having a bit more Asian affinity than Finns, about the same as Balochis or Kalash or Brahui people, and are closer to the Finns in their level of East Asian affinity than they are for'ex, Uighurs.
Based on this genetic distance, I expect their phenotype difference from the farmers of the time was on a similar level to the present day Balochi-Sardinian difference, in its size, and a bit more than the present day difference from Sardinians-Finns. Could've been more though.
Reconstructions from Mesolithic Europe generally don't look as extreme as RR's hunter image, although he is definitely right about the wider faces (not sure that Mesolithics had wider noses). But there is a degree of interpretation in them that might bias the reconstructers towards current phenotypes.