My CTS handles like a dream and has plenty of power. 0-60 it is great, when in "sport" mode. I can take corners that are posted 35 mph at 55 mph. I have the 3.6L with the 5 speed auto and it is plenty fast. I have two beefs, though. The XM radio has static, which I thought was impossible on satellite radio, and apparently all CTS's with the single CD player do, too. The response from the dealer/GM to fix it was underwhelming to say the least. It still hisses. The battery was replaced under warranty today because it died twice and I had to jump it. Yep, the car has 7,000 miles on it and the battery died.
The memory seats, leg room (I'm 6'1"), overall comfort, auto sunroof, and the self dimming mirrors. The leather on the seats is very luxurious and the mesh parts to keep your back cool are ingenious.
Clear up the static on the XM. Bring the steering wheel out a little bit or telescope it for us tall folks. The computer doesn't know the tire pressures, but my LT Suburban does. Since the stereo has AM, FM1, FM2, XM1, and XM2, install a source up/down button.