The IS is designed to be a sport/luxury vehicle. It is also a relatively small car, and as a result of those two points, you will feel more of the shift than you would in a larger luxury car. What did you drive, a Lincoln, or a Mercury? What model was it? The size, power, and suspension would make a big difference in the feedback you got from the car. Ford/Lincoln/Mercury vehicles have been notorious for having pretty mushy suspensions, with the exception of the Mustang, and maybe the new Mark and 500 platforms.
That said, I have to also say that I don't feel the shifts in my '08 250 very much, unless I have my foot deep into the long skinny pedal... but then, when I do that, I am usually taking the revs up, and paddle shifting. However, when I am driving more aggressively, I do notice a lag between depression of the gas pedal, and reaction of the car. Part of that is the traction control. In new cars with auto trans, it is very difficult to spin the rear wheels... but I digress.
Correction: It was a Mercury Milan. I guess I will have it checked on my next service date.