Touch ID is great, my iPhone 6 is the first device I have used with it. It varies, sometimes it unlocks so fast the screen is still fading on when the animation is going, and other times it is a bit slow, or throws a "Try Again".
Sweaty or just slightly clammy hands screws with Touch ID the most for me though. That probably is when I get 75-90% of my Touch ID failures. Stinks though because I am a pretty nervous person, and my biggest sign or nervousness is clammy hands.
Touch ID is still a pleasure to use nonetheless. Still haven't been able to make an App Store purchase with it though, I don't get apps too often and usually my phone has been restarted by the time I decide I want to download an app again.