First I want to thank ehren37 for actually writing a review with specific reasons why he didn't like the plastics. But I am also going to have to disagree with you.
I ended up either winning or buying every single Arcanist model at Gen Con this year and have been blown away with the quality. Things like the wood grains on Mei Feng's exploding wood, the feet of the Rail Golem, or Willie's wheelbarrow or Willies grin/teeth. This are things that would NEVER be that crisp or clean (or even possible) to show in metal.
The plastics where also much, much, much, much easier to clean up. In the time it took me to remove all the mold lines from 2 Gunsmiths I was able to clean the entire Rail Crew + assemble a couple of them. Add in being able to use plastic glue and the fact the pieces are lighter I was able to spend less time holding pieces together and more time gluing things together.
The only issue I had was on a couple of the really small joints putting a little to much plastic glue on. While I didn't lose any details or anything, I could see people touching the wet spots and leaving fingerprints. The big things is you REALLY should go buy good plastic glue for putting these plastics together. Some of the seams are very small, and trying to greenstuff them would be a giant PitA. I personally swear by the Testors plastic cement. The bottle I have has put together almost 200 Ork soldiers + vehicles as well as 250 Skaven + big things ans is still going strong. http://www.testors.com/product/136635/3507AT/_/Liquid_Cement_1_Oz.