I was using a Acrylic material from 1.9 on some of my parts that are natural Polypropylene which is semi-transparent. This gave me a pretty realistic effect. I have tried reproducing this material in 2.0 and have had no success. For reference, I overwrote my 1.9 materials on install. I had a demo version of 1.9 on another machine, and was able to get the material settings for the Acrylic out of there, but in using these settings in 2.0 the effect is not the same, no apparent transparency.
The materials are the same. What material are you using?