I've only had this a few days, but I am happy with it so far. Sound quality is acceptable, likewise mobile signal strength - though wifi reception is not quite as good as my other gadgets. jelly bean is on its way, apparently, but I'll probably wait to see what others say before upgrading! I'm hoping that jelly bean will get rid of some of the Samsung bloatware; the only Samsung extra I find useful is the Kiri utility that allows me to sync my phone with selected Outlook address books and calendars, without having to rely on the cloud.
by the way, despite what you might read elsewhere, the box for the SIM-free version does NOT come with a black back cover - so if you don't like the virulent yellow invest in a non-transparent protective skin. Also, there was no headset; my guess is that the extras only come with the branded versions. The headset socket is a 4-pole one; you can plug in a standard headphone with a 3-pole plug, and of course there are lots of bluetooth solutions - or you can use the speakerphone: it's OK for use indoors, but I have not tried it outside or in a car.
Of course, this is a budget phone, so it does not have some feature premium models often have: for example, the ability to access home servers for file access, media streaming, etc; HDMI output; OTG and docking stations; optical zoom and a LED flash. On the other hand, it is easily pocketable, reasonably priced, and supports USB and wifi tethering (but not reverse USB tethering: useful when travelling, when you don't want high roaming data charges or to risk the open wifi network provided by the hotel, and instead you would like to take advantage of your laptop's secure internet connection).