I bought the STS because it fit our wants when shopping used cars: luxury, comfort, cheap. Poor resale value has worked just fine for us since we can buy a little more car for the money on the used market. Overall, I like the styling of the STS inside and out. Many prefer the CTS in both respects, but I prefer the toned-down design of the STS. I am not normally an extended warranty fan, but anybody considering the STS would be wise to find one under factory warranty, or in the case of a 2005 or 2006, a factory CPO warranty. Many little problems crop up. Take reviews here with a grain of salt. The 'high-end' stereo is NOT all that and is easily trumped by a decent aftermarket ones.
Exterior styling, smooth acceleration, wood accents, heated/cooled seats, no major failures.
Nearly useless Voice Recognition (VR), Nanny DVD, Nav and BT interface (cripples system when car is moving, hint: buy a kit and disable it), abysmal gas mileage, average seat comfort, relatively poor legroom in rear, many minor issues pop up