I personally am on the fence about the Nexus. I think the size and shape feel great in the hand (I know, that's what she said...). I do think it feels a bit light and somewhat cheap / plastic, but I understand the choice of plastic being a durable material for using on a phone.
I traded in an iPhone 4s for the Nexus, so in comparison, I think the iPhone (material-wise) feels very top-notch. However, it is blocky and doesn't really feel that great in the hand. Plus it is glass on both sides so... durability? Although my girlfriend's iPhone 4 has survived quite a few drops just fine - so I think with any phone the biggest durability concern should be the screen.
Either way, quality of materials was a trade off for me that I didn't mind. Nexus fits my hands better, and I missed android! Plus, with the iPhone 4s I had, I constantly was paranoid about dropping it, where with my Nexus I at least only have 1 chunk of glass to worry about.
DancingNexus