I upgraded from the X on launch day and overall, I have to say that in most cases I do see better performance. However, I have noticed a few symptoms that I thought it was just me or the local network. Seeing other people's comments here it seems that it is something more widespread.
Here are the symptoms:
- device occasionally searches for network (searching bar animation is displayed) even in areas with strong signal
- 4G/LTE data connection stalls. Toggling flight mode on and off restores the data connection for a few seconds, then it stalls again
- uplink may be poor under certain circumstances
It sounds like some (if not all) of the above are due to software issues. It is the first time they use a 4x4 antenna setup, so maybe they didn't get everything right on the first iteration.