Have just exchanged my 06 plate 220d for a BM 320d touring which I initially considered simply because it offers a bit more luggage versatility. I had recently had a 2009 220d on loan and whilst it was a bit smoother than my old car I have to say not much, and I really felt Lexus have cheapened some of the interior trim on recent models. I did a back to back test with both the BM 4 cylinder 320d and the 6 cylinder 325d but frankly the 4 cylinder amazed me with its smooth refinement that I just couldn't see a significant difference between it and the 325d. Its much better than the Toyota unit. I'm sure the 330d is well worth having if you want to spend nearly 40 grand with options.
The BMW engine is much quieter, smoother and more flexible. I don't find the run flats unforgiving, on the contrary the car is more cushioned over poor town surfaces than the Lexus ever was, there's less road noise and no wind rustling around the door gaps like the Lexus. Yes the interior materials are a bit cheaper in places, the optons cost a fortune and unfortuantely the world and his wife have one, and yes I will miss Lexus sevice which has been superb, but a 320d touring gives you a bit more flexibility luggage wise and genuinely is a more enjoyable drive with sensible gear ratios to boot!