I happened to rent Impala LTZ for a week and wanted to share my experience.
Impala has enough room in the front seats but back seat is not large for the car of that size. If you carry large adults in the back I would go with another car. Hyndai Sonata had more room in the back although front seats probably not as roomy.
Trunk space is especially ample. We could fit large stroller and 2 suitcases in the trunk without any problems. Very happy with that, since that is why we rented a large car.
Suck big time. Especially bad is placing all controls on one nob on the left side of steering column. It is not intuitive and hard to control. I prefer two knobs on both sides of steering column.
Climate control is a joke. There are two small levers which move in very fine increments and are impossible to adjust in the moving car. Radio has convoluted controls. Hyndai radio for example has more functions and very easy to control.
Fan output control has 2 steps for every picture and you are not sure if you selected the right output since the indicator is pointing to the same picture.
One thing that I liked was on board computer. It has a lot of information and even tire pressure in each tire. I did not play with it too much but it had lots of options. Radio played MP3s but would take extra long time to read the content of CD. I had to power it down and up several times to get it to work.
Keyless remote had engine start button but the feature was missing from the car. They should have remote without extra non working buttons.
There are 3 outlets including one in the center console, this is good since most cars only have 2.
*** Build quality
Build quality is mediocre. The fake wood panels look out of place. Over all this is typical American car that lacks refinement of Camry or Accord. Black rectangular radio in the wood-like frame looks ugly, especially because frame is different shape from the radio. Ford had same problem with their radio.
Leather on the seats is nice quality. Although seats are not that comfy. My 2009 Sonata has more comfortable seats but leather isn't so nice. Both front seats are powered which is nice.
No complaints there. My car had 3.9L engine with plenty of power. Transmission was shifting smoothly and downshifting on time. If you are after performance car this may be the car for you. If you are willing to sacrifice in all other departments.
*** Fuel Economy
Fuel economy is bad. The car is rated to 27 MPG on highway. I do not know how they rated it. I think it will get 27 MPG if you drive it at 50 MPH on the flat road. We took it to LA from San Jose which is 360 miles ride on the flat road with some mountains at the start and at the end. Fuel economy was 23.8MPG according to on-board computer. I did not speed but went around 75MPH on flat area of HW 5 and around 60 in the mountains. I think the transmission needs another gear or two to improve fuel economy. The turning off cylinders does not help a lot and mileage drops to single digits as soon as you press on accelerator. The price of the gas for round trip was around $110.
We have rented Ford Crown Victoria before that had better mileage with V8 on that same trip. I was expecting around 27MPG at least with my driving. My Sonata is rated at 32MPG and I get 35MPG out of it as a rule. Sometimes even 37 if I only drive on highway.
Ride is noisy for the car of that size. I could not hear our kid from the back seat. This is not a whisper quiet Camry or not even Hyndai Sonata, which is reasonably noisy. Maybe they wanted more sporty feeling, not sure. Handling is ok in my book, but I am not race driver.
*** Over All
There is not much to like about this car. I would not buy it or recommend it at all. GM definitely has a long way to go before they build a car that can compete with Camry or even Hyundai. I have not driven Avalon which would be in the same class as Impala but our V6 Camry is much better in all aspects although Toyota is starting to cut corners as well.