1. One is regarded as having one of the best, if not the best audio quality via headphones and loudspeakers (no phone comes close with the loudspeaker, just can't beat front facing stereo speakers that have dedicated amps)
2. Far better, the one has the best mic. on an android smartphone by miles, using nokia's tech.
Although, once HTC's stock with that mic. tech runs out they have to find another mic. to use, no idea if this has happened yet and what it is being replaced with
3. Better overall compared to the nexus 4, main areas being a much better camera app, way more features, better hardware overall, main areas where it is better will be faster focus, capture more usable shots (due to OIS and very fast shutter), wider FOV, superior image stabilisation, superb macro and low light shots etc.
Only downside is lack of MP so cropping/zooming in won't be as good.
4. imo sense is the best skin by a long shot compared to stock and every other skin
- better unified feel throughout in terms of app layout and colour scheme
- some of the apps are amazing and imo no 3rd party apps are as good, such as the browser (quick thumb controls + flash player works + very fast and smooth + plenty of options + text reflow when you pinch to zoom and double tap), gallery and camera (feature rich)
- fastest and smoothest skin to date imo (even better than the nexus 4 from my experience)
- looks nice, has a minimal clean professional look throughout
5. If you're rough with the phone i.e. throw it in a pocket with keys, coins etc. then it could get scratched
There are videos on youtube where it holds up very well though....
But if it does get properly scratched then yes you will see the "raw" silver aluminium, if this happens, I find a black sharpie works great to cover the marks up
Overall the build quality is more or less superior to the nexus 4 (QC issues is a different matter) and if you have a tiny gap where the speaker grille meets the rest of the metal body, this is normal, not an issue like many say, it is not part of the CNC machined body thus is stuck on with glue, only be concerned if it feels lose and the gap is actually 1mm or bigger!