While the CTS is the darling sport sedan from Cadillac, the STS was a more refined car with more room, and power (with the NorthStar V8) and better egronomics with regard to the memory seat and wheel recall functions. We have both a CTS (2008 premium ed) and an STS (2009 Platinum ed), so can compare them both. We also had a 2005 CTS and two (still have 1) LT1 Fleetwood Broughams, so we've had a few Cadillacs in recent years
Handling and performance are equal to or superior to the CTS, particularly with NorthStar & the wide 255mm 18" rear tires (CTS has 235mm front & rear) Interior room is better and the single glass sunroof is quieter.
15 speaker Bose system is very powerful and clear.
The NorthStar V8 is the best thing about the STS. With RWD it is a wheeled rocket. The 15 speaker Bose system outdoes even the superb 10 speaker CTS system, and the Platinum edition's suede headliners, all leather interior, chrome wheels (with wider 255mm rear tires) make for a one of a kind vehicle. I have not seen another on the road yet. The platinum also comes with the loaded option group with all the electronic frippery that GM could muster, like adaptive cruise control, side blind zone alert and lane wander warnings for those of us who can't stay in our lane! Front seats are nicely laid out with more room than CTS. The cooled seats are very handy in the summer which lasts 9 mos in FL!!
I would like to see the cornerning lights brought back, as well as the power trunk pulldown, and the parking break auto pulloff. The seat should NOT move forward until the engine is started. The wheel refrains from tilting until engine start (that is a good thing, just wish the sat would do the same).
A bigger glove box that holds more than the owners manual and a tire gauge would also help. No complaints on power or handling or interior comfort. It would be nice to be able to use the same remote for the 2008 CTS and the 2009 STS.
Finally I would like to see ENGLISH WORDS on the controls instead of annoying undecipherable icons or symbols, eg, seat heater instead of a confusing symbol.