I saw a video from MobileTechReview on the HTC One M8, where Lisa pointed out the metal can be more affected by temperature changes than plastic. Yesterday I held several phones in an air conditioned store. The M8 was noticeably colder than the other, plastic backed phones. That could be uncomfortable outside in the winter in the northern States. I think that it's not just "plastic=bad." It's situational, and the type of plastic. The S4 just seems cheap to me, where the S5 was pretty good.