Android, the very famous mobile OS which runs in millions of devices has seen a tremendous growth in recent years. Every 7 out of 10 people I know use smart phone which is powered by android.
Android is so easy to use that people easily adapt to it. With the latest version lollipop, android has seen a huge growth. Companies like Samsung, HTC and many more depend hugely on android for their market growth.
I should say there is not much need for providing a skin over android to sell a device. I am not a great fan of Samsung touchwiz or HTC Sense. Stock android is cool and has the benefit of faster update to latest version.
That being said, let me share few pointers where people get upset with android. Android being a huge project and we see lot of developmental changes, bugs are common and with regular software updates it can be resolved too. I am talking about certain bugs which android didn't provide any fix as such and the people who got affected by it are still furious with Google for ignoring such cases