The auto gearbox works superbly particular on the 335i. I would say that the manual gearbox is less in keeping with the car than the auto is. With the relentless acceleration the 335i has, both hands need to be on the steering wheel - having the auto with paddles worked brilliantly.
The gearbox was a teeny bit sluggish at low speeds in high gears, but get over 15-20mph and in every mode it was brilliant. Sport manual changes were quicker than i'd ever be able to do in a manual, and very smooth. Changes in D were perfect. I can't really think of anyway it could be massively better? Obviously the newer ZF 8sp gearbox is quicker in nearly all circumstances, but the 6sp ZF is still very good indeed - and most importantly, far and away from the "slush box" autos of old.
The behaviour of the box *did* change a lot between software updates. When I first got the car, when it was on like an 09 software level, the changes in sport/manual were very harsh and jerky. Then when the software of the car was updated, these became so much less jerky and quick.