I've been on stock Android since before the T-Mobile G1 was released. The new HTC One (M8) is the first time I've experienced the joys/horrors of a third-party skin in my day-to-day phone. I was anxious, especially after seeing Touchwiz on my wife's Note 3.
Sense 6's built-in apps are both more attractive and more usable than their peers on Nexus KitKat. I'm thrilled to avoid the broken time picker in the nexus Clock app and the unusable radial-configuration of the default Camera app. HTC's quick settings is customizable so I could give Wi-Fi hotspot easy access.
Sense 6 is Android refined. I highly recommend it.