Quick tip: if the Digital Crown on your Apple Watch all of a sudden1 feels too tight and doesn't turn smoothly, probably it was somehow over-turned (and probably because you played with watchOS 2 Time Travel, as I did). I don't know how that happened because it's clearly not supposed to happen, but turning it in the easy-to-turn direction for a few rounds fixed the tightness issue for me.
There's also an Apple Support document on troubleshooting and cleaning the Digital Crown, if the above doesn't help.
Especially after upgrading to watchOS 2. Why in the hell could upgrading the software screw up the hardware? You'll see a possible cause if you read on.↩︎