Samsung Fridge/Freezer: Seemed to work fine for a year or so, then we noticed that after any power outage, it would tend not to cool things when it turned back on. We'd notice that the temperature indicators on the front were happily announcing that the fridge was at 60F and the freezer at 40+. (Unplugging it and plugging it back in again would usually get it working again). Now it's even worse, the temperature indicators show things working just fine, but the actual temperature inside is either way too warm or way too cold and everything in the refrigerator is frozen. Unplugging and plugging back in will usually make the temperature sensors show the actual temperatures, but there seems to be no guarantee that the actual problem will be resolved and it may need to be unplugged and plugged back in a few times before it works correctly for a while. Getting rid of this awful thing very soon.
Samsung "point-and-shoot" camera, seemed to work great when I picked it up and took it on vacation, but when I got back and downloaded the photos to look at them on a real screen, a circular area in the center of every picture was out of focus: Lens defect. Got it RMA'd right at the end of the warranty period, the third-party losers they outsource it to kept the camera for two weeks, then sent it right back with a note to "make sure the battery is charged when you use it.". WTF?
Samsung "Mesmerize" phone (Galaxy S variant), cell/wifi/bluetooth would all just die and stop working until completely powered off (not just rebooted). To be fair, the one that I got as a replacement worked reasonably well.
Samsung Galaxy S4: I actually mostly like it (still using it), but sometime in the six months after I got it, the USB data port stopped working. I'm not sure when it happened because I can still CHARGE over USB, and I usually do file transfers by SFTP rather than a cable so it was some time before I even noticed. Haven't bothered trying to get it replaced because it otherwise is working okay on "Optimized Cyanogenmod".
Before anyone asks "If they suck so bad, why do you have so many Samsung devices", it was a few years between the fridge, camera, and Mesmerize phone before the pattern became obvious. I actually was reluctant to get the S4 but it was the only model my cell carrier had that was moddable.
tl;dr:Samsung's hardware quality control sucks, and they plainly don't really care.