We bought one of the FIRST 2006 Chevy Impalas literally right off the truck. There were a few "niggly" things that did not work out, all of them related to a "new design". Importantly however, this was not universally true!
The first issue, more of an annoyance, the sun visors would not stay up after the first 6 months, further the covers on the visor mirrors warped and no longer closed.
The water pump quit at 68,000 miles (after market was not available so this "Chevrolet water pump" was right pricey).
The power steering pump at 71,000 miles, likewise on "national back-order" so the pump was REALLY expensive.
I have noted this comment elsewhere, but it is worth mentioning, the transmission scared the hell out of me! I first noticed the issue with about 1500 miles on the car. When it was put in drive, occasionally it would not engage cleanly, when one stepped on the gas it would grab. With most transmissions such an event portends and impending disaster. I was reassured several times by the dealer that it was "nothing". They were warned if this documented problem failed with a temporal relationship ANYWHERE near my warranty expiration, I would let them meet my solicitor. As it turned out, the transmission otherwise performed reliable and smoothly AND it never did fail in the subsequent 70,000 miles... go figure.
I have always avoided the "first edition" of anything (who remembers the first GM front drive cars from the 80's?). However, I went to the dealer that day and test drove my LS. It was smooth, comfortable, quiet and QUICK.
My favorite demo was to cruise up the interstate and ask the passenger, "how fast do you think we are going?", the answer was always, "OH 70 maybe 75". I would then smugly reply, "guess again, I'll give you a hint, look at the display!" So while driving with two fingers, chatting in a conversational tone the passenger would lean over and see, "North American governed speed 108 mph" and say something like, "Holy Smoke". As an aside there was PLENTY more RPM before it came close to "gearing out"
We consistently got 29 to 30 on the highway... even at rural Kansas speeds of 75 or 80 mph.
It was a very good car and I knew Chevy would fix the issues.
I bought a 2008 Impala SS and have completely enjoyed it... so at 20,000 miles NO issues what so ever... so far. The mileage of the SS is not great, BUT I did not BUY it as an economy car. I bought it for the V-8, one must remember there are certain rules of physics and thermodynamic that one cannot get around: If you want the ponies, one must be prepared to FEED them!