My thoughts after a week..
Call quality is good. Nothing to necessarily boast about, but no negatives to report. 75% more than loud enough for me, no complaints about quality on my end.
Speaker sounds good, again nothing to really boast about. I usually don't listen to music from the speaker - podcasts, occasional youtube - so I can't really offer up any detailed diagnosis. Definitely sounds better coming from my Galaxy Nexus, and more than suitable for my daily use.
As for headphones.. I have a decent pair and a crummy pair and they sound comparable with my other devices and music. I mainly use my Jaybird Bluebud headphones and absolutely zero complaints. 16 Ohms* for reference, and they sound great, but I haven't heard any unusual reports about headphone consistency anyways so whatever you have should translate in quality (source consistency provided). Bluetooth issues and 4.4+ seem to be more consistent with speaker setups / car use but don't quote me, but I've had no bluetooth issue between 4.2.2 and 4.4 and my headphones. Can't comment on other bluetooth compatible issues.
Can't find anything in this department to fault the device on, personally, but YMMV, of course