I've been a loyal T-Mobile customer for over 10 years, the last 8 without a contract. So I've been able to leverage my status as a long-time user to secure for myself an outstanding price for my unlimited data plan that no other carrier comes remotely close to matching. That said, I got my G2 on Sunday after my trusty Amaze was stolen from my car on Friday night while fueling-up on my way home from work.
I walked into the T-Mobile store with the intention of getting a Nexus 5, but left with the G2. For the same price there is no comparison. The longer battery life, better sound quality and camera, along with the doubled storage capacity sold me. I personally can't justify spending more than 400 bucks for any handset that will be obsolete in a couple of years and with performance and features that rival those devices that cost over $200 more, I thought it was a no brainer.
As far as the comments about lack of development are concerned, it doesn't bother me. I plan on compiling my own Cyanogenmod, Pac-ROM, and Evervolv as soon as I get bored with stock and get time off from work. Besides, in the few days I've used this device I've found its OS to be one of the best stock Android I've ever used (I like it way more than any version of Sense that I've used). It doesn't deviate too far from ASOP yet has additional tweaking that is normally only found in custom ROMs. In fact, if I can get some time to figure out how to root and install a compatible aftermarket recovery, I might just deodex and debloat it and leave it as is for awhile.
As I said, at its current $398 price point it's got more bang for the buck than any of the other handsets T-Mobile is selling.
Just my 2 cents