I just picked up my ONE and thought I would pass along some information that might help others and may help those trying to make the decision.
I was not sure what to expect when I took it out of the box (did this at the Sprint store). First thing I noticed when I picked it up was the weight. Compared to the OG Evo, this thing is downright light! I is so light I have a hard time thinking that anyone would want one lighter (SG4 for example). Despite what others have posted, I did not find the phone too slippery. That may have been due to my sweaty palms because I was so nervous - like holding a newborn baby. The build quality is what others have posted. Nothing short of - WOW. I can confirm the gap issue that others have reported. I did not like the gap size on the first one they opened, so they were willing to open their only other model (it was spoken for already, but they opened it for me). This second one looked much better with a very very slight gap on top. Nothing like some of the pics being posted. No rough machining noted at all. I told them I would buy if they would give me this one and they did.
I wanted to comment on this one in particular. Despite what others have posted, I did not find that the notifications and ringing were too loud on the lowest setting. Now here is the kicker. When I got home, I thought it only appropriate that I initiate the ONE by playing the Tolkien trilogy soundtrack and the trailer from The Hobbit. Yes, it does sound good, but I had to turn the volume up to max to really hear it well. I am wondering if this phone has an update that brought the volume capabilty and levels down. I find myself wishing that it would go louder.
I have only made one call. The quality was so so. Since the person on the other end has an Uma landline, that may have been the issue. Not sure, yet.
I haven't enabled GPS yet, but the phone still did a good job of finding me in my house. It was only off by a hundred feet or so. Not bad.
The Hobbit trailer looked fantastic. The comments that have been posted by others are spot on. I don't have much to compare this to, but my personal opinion is that this is amazing.
The only negative so far
There was one thing I was not happy with at all. Maybe it is a setting, but I seem to remember something like this back on the OG Evo. When you go into the call screen, below the word Phonebook, There is the word HISTORY on the left and FAVORITES on the right of the screen. However the first three letters of the word HISTORY are faded in color - almost black and you can barely read them. The last two letters of the word FAVORITES are completely off the right side of the screen and the remaining letters RIT are faded just like the other side and barely readable. I am not sure what is up with that or if it is normal. I will let the others chime in and advise if their phones do this. That's it. That is my only negative so far.
There is much more to play with and get set up, so I will post more when I have it. If I were to advise anyone on the fence at this point, I would say that it is worth pulling the trigger. Go for it.