I just ordered my second one (white 32GB), since my oldest has taken the teal 16GB I bought here a few weeks ago.
The build quality is *outstanding* at this price point, and actually really good at any price point. It's a very solid device.
Apps are, well, web apps, so mostly you need to be online, but you can use media files (movies, PDF files, music, etc.) on the local drive or via the USB slots, even when flying. Battery life is fantastic - 7+hours with typical use.
T-Mobile setup was easy-peasy. I upgraded to the 1GB/mo plan simply so she can use it to do homework, but you absolutely don't need to use cellular, and even if you don't expect to, set up the free plan. It's... free. Why not have it there, just in case? Sure, it's not a lot of data, but that time you need to access email and the wifi isn't working (power outage, say), it's worth it. And, again: free.
I'm going to set up multiple booting options on the new one (played with them on this), and, given how easy it is (just follow the steps online), it's a great way to get additional offline functionality and turn this into a more powerful system.
That said, as long as you're online - and most of us can be, most places, most of the time - this is a great system even if you never modify anything about it. I was very pleasantly surprised, and I own a couple of older Chromebooks as well.
Get one before they're sold out again.