Is yours the Stronic or ZF? On the V6 lower powered models I think it was Stronic but above 400Nm it is the 8 speed ZF I believe.
I've had 2 Stronic boxes and both have been fine. I just leave mine in the Auto driving mode most of the time as it seems fine for most purposes.
Some people complain of lag in certain situations, usually when the box thinks it is going to down change to a stop maybe, but then you go for a gap in traffic and it doesn't respond immediately. But you can always use the S setting to improve this, or just override with the paddles for short periods like when overtaking, that's what I tend to do, as then it is like a manual. It will then revert to automatic after a short while, or you can force it with the lever.
Overall very good gearbox, but I always think of it more as a kind of auto manual rather than a conventional automatic, which I always disliked previously.
I like the intelligent coasting feature as well, works really well on fast roads with small inclines, so you lose less speed downhill due to unnecessary engine braking.
