I bought this phone as a gift for my dad, he is using this phone from the past 5 months and I am telling you there is not at all a single problem in the handset, apps runs smoother as compared to my nexus5, multitasking is awesome, ram is pretty smooth, there is a little heating issue thats it, otherwise all the games I installed in my nexus5 are running in karbon smoothly, or I should say even smoother than the nexus.
Picture clarity is wonderful, as during the daylight you can easily trust the camera, little noise and blurred images are there during night overall a good camera, talking about the processor, quadcore is doing its work nicely there's no lag during switching apps especially while chatting and playing games at the same time or even doing online work, talking about the looks, it looks gud and handy, plus the 5inch display is decent not too big like a phablet or not too small , you can carry it your pocket with no problem.
Overall a great phone except the battery backup is not that good as compare to its competitors, if you are planing to buy this phone in my opinion go for it with eyes closed it will not disappoint you.
