The 2011 Chevrolet Impala has ample space for people and their bring-along stuff, but it's nowhere near as sophisticated or as well-tailored as its American and Asian competition.
The Impala does offer plenty of interior room, along with a generally quiet interior. The front seats are of the wide, flat variety--perfect for fleet duty but because they lack good bolsters, they're only truly cozy for long-haul interstate driving. And while headroom and shoulder room are plentiful, there's not as much leg room inside as you might find in the Toyota Avalon or the Hyundai Azera. It's the same story in the back seat of the Impala, though the back bench is one of the lower ones in its market segment.
All the retail versions of the Impala have folding rear seats that open up the trunk to the cabin. It's already 18.6 cubic feet back there--not quite up to the Ford Taurus' 20 cubes, but large--though the Impala's trunklid cut-out makes it a little less cargo-friendly than it could be.
A few years ago, GM revamped the Impala's interior. It made the leap from commercial-grade to retail-grade, but it's still one of the less nice places to be, particularly compared to the Azera and the Taurus. The plastics are more plasticky; the cloth seats can be swapped out for leather, but the hides are of the shiny variety. To its credit, the Impala allows almost no road noise to permeate the cabin, just a little tire and wind noise at extra-legal speeds.