I've had good experiences with manually initiated lane changes, a little less with NOA-initiated lane changes. The main weakness I've experienced is a willingness (on NOA) to change right into the path of a fast closing car. While maybe not precisely dangerous, it has to be annoying for the other driver. I assume a manual change would also be willing to do that, but hopefully I'm aware enough of the situation not to initiate it.
The most obvious problem with lane changes has been its tendency to abort the change, sometimes for no obvious reason. Sometimes it seems to be reacting to a car in the next lane over from the one you are changing to, as if it is not sure which lane that car is in. Recently it has been doing very well (at least with HW3 in our Model 3), so maybe most of that has been eliminated.
On the good side, when it first came out I was driving with NOA and unconfirmed lane changes near Arlington, VA in heavy traffic and depending on the navigation for directions. Turns out I had to enter a freeway from the left, cross about three lanes, and exit the freeway on the right, all in the space of about one city block. NOA was a champ and made all the lane changes and the exit without a fuss. I would have missed the exit as I was checking what the next turn should be on the nav.
That said, some of the poor lane change choices NOA makes led me to switch back to confirming them. I'm much better at confirming than canceling.
