I've moved to the lex from a BMW 323 (E36). I think they make brilliant cars and are an even bigger marketing success. Even so I think the real 3-series to buy are the 330 petrol/diesels and the M3. Cracking cars. People drive debadged 316/318's only for the sake of being in a beemer and inspite of the fact that the engines arent bad, its kind of missing the point.
The amount of kit, a bit of uniqueness and customer services made me buy the Lex. All the IS needs is slightly better low down torque for the IS200, a 2.5 litre petrol and a 2.5 litre diesel and I bet you BMW will have a serious contender on their hands. The fit and finish on the Lex is on par with the BMW's and Audis; what it probably lacks is European flair in the cabin design (but thats what sets the cabin apart as well).