Android devices may seem shinier when they are new. When I got my OnePlus One, I thought it was the best phone ever. Came lollipop upgrade, it turned into one of the worst phone I've used. Even starting the camera lags. System UI forecloses. The phone became only a nice shell of its former past, with junk software inside. This story is similar to most Android devices.
Having said that, a clean reset of the device usually freshen it up. Problem with Android is, there's no easy way to restore your phone like you never left it. With iPhone, if I had problems with it, I would simply back it up through iTunes, restore it, and it's like I never left the phone. On Android, you are forced to do the dirty work in backing up the content of your device.