I am very happy with the coverage, prices, and customer service. I am not so pleased with the choice of handsets nor their slower EDGE network. Thankfully, TMO is slowly rolling out their 3G network and thanks to GSM technology it isn't too hard to get an unlocked phone I like. In addition, TMO tech support is very kind with helping me set up data settings on a non-tmobile, unlocked, gsm phone. Which reminds me - TMO gladly provides you with the unlock code and instructions for any TMO phone.
Before I shutup, just thought of something else - thanks to UMA (wifi) calling, I can make calls over wifi if the cell signal is iffy or m.i.a.