I actually just got mine yesterday from my local AT&T store. So far, it's not a bad device. There are some definite quirks with Dynamic Display. Also, 3rd party launchers seem to have major issues going from phone to tablet that Dynamic Display can't handle. I've been able to root it using towelroot, but I don't have a custom recovery for it yet.
All in all, the device itself is pretty solid and works nicely. No real lag that I can see (yet).