I purchased my Nexus 6 in January. Things went fairly well for the first couple months and then started getting issues with the ! showing up. Started to happen a few times a week then progressed to sever times a day. That and when I'm out and about (DMV, grocery shopping, paying bills, etc.) my phone would say LTE but couldn't load pages off the net. Speed tests resulted in getting super slow speeds.
I had the N6 replaced via RMA. My next N6 had the same issues. Couldn't read the SIM card, no data, yaddayadda. Was sent out a THIRD N6.
A few days ago my N6 got that dreaded ! again while at work. My wife had been trying to reach me for nearly an hour. She's 8 months pregnant and fell. I didn't know she fell until a coworker found me at work to notify me I had an emergency call. I basically blame this phone, or the Nexus 6 anyways, for the delay in her getting ahold of me. She's alright, but Jesus, if she went into labor, I don't know what I would have done. I almost always have excellent coverage at work, but this phone struggles where every phone previous never had. Been with T-Mobile for 9 years. Been working at the same area for 5 years. I've had a Galaxy S4, Nexus 4 (absolutely LOVED LOVED this phone, still use it too) Nexus 5 (also loved this phone as well) and have never, not once had problems as bad as I have been having.
With that said. I will miss the gorgeous screen. I loved the front facing speakers. I'll miss the pure android experience.