Can't compare to the Pre 2, but it's much better than the original Pre. Much more solid feel (the Pre- would sometimes reboot when opening the slider!). I've never had a problem with the unlock button.
I have both here on my desk. The Pre 3 feels a lot slicker, and has a lot nicer feel to it in general. Also it's shape is a bit more modern. In general I would say the Pre 3 feels a lot more expensive and steady compared to the Pre 2.