I'd disagree with this and some of Will's comments. In the US Lexus is more highly rated than in Europe. One of the reasons for the poor showing in Europe may well be the fact that Lexus had no Diesel engines and when it did get one, there was no auto option and it was a poor 4 pot. Just think about the number of prestige auto diesels that are sold in Europe. When you miss a huge market like that, you already losing.
I'd also say the previous IS was a match for the c class of that era, which was a pretty poor car when taking all things into account.
I' also think BMW/MB cars are bought by just as many people because of badge snobbery as by people that actually prefer the cars. Which is why these manufacturers get away with so much: they don't have to try hard to sell their cars. I'd also suggest that if it Lexus was not around, then a lot of standard kit would still be optional. As for reliability/dealer service there really is no comparison.
I find most poverty spec BMW/MB cars pretty soulless, and it's only untill you get to the higher end models with more kit that you think "yes, nice car". But if you are looking for a car to get you from A to B, with as few ownership issues as possible, then it would be Lexus all the way