It has irritated me for years at how Siri has such a delay when using it on the watch. It's very useable, but always feels a bit too slow. Actually I find this when it's connected to the phone. If I'm on a wifi network without the phone nearby, or on cellular, Siri is much faster. I wish the watch could just act like an independent device at this point.
Anyway, those two features (Siri and double tap) tempted me to upgrade from my Ultra, but I'm going to wait I think.