There's an in-depth test, analysis and praise in two parts of the phone on AnandTech.com for people who know what to look for in a smartphone. They recently also did their first part of the Samsung Galaxy S4 test and should've considered the HTC One when comparing the two at some point.

The black phone wasn't available in my area at first and I don't have a service provider contract yet, so the only thing I know about its network performance would be that WiFi works when in immediate vicinity of a router providing it. Fascinating, I know.

4G should be okay when it's offered, but it doesn't seem to be usable primarily with strict and sparse bandwidth caps and radically reduced speed and sometimes additional data volume charges once over the alloted amount.

The 1080p screen looks really good to me.
VLC in a beta for Android provides good and rather flawless playback of television material of the 1080p Web DL category Apple offers on iTunes or 1080p porn clips from Brazzers, for example.

I prefer CDs for their uncompressed sound. Usually, not all desktop media players can play back a mixed DJ performance when extracting the audio in separate tracks without gaps in playback when the track changes. Extracting audio with Exact Audio Copy and playing it back in Windows Media Player works on desktops; on the HTC One the integrated player works just as well, VLC doesn't for gap-free audio as pointed out.

Beats Audio seems to be a rather useless bass attenuation, thus an equalizer preset, possibly for the rather useless Beats Audio in-ear headphones I won't use.
The headphone jack seems to be an okay one; it doesn't sound terrible.

The camera I didn't try out extensively; the test mentioned above should make things more clear for the interested.
1080p video seems to be offered and some video effects presets are ready to annoy.

25GB of internal usable storage is the fixed capacity in hardware on the 32GB model. There's no SD card slot and HTC seem to want people to upload to Dropbox or whereever else when they need to. Happy data transfer then.

It's not bad.