The Sienna is a large minivan, at 200.2 inches long, riding on a 119.3-inch wheelbase and sitting at 78.2 inches wide. It's marginally bigger than the prior version, and roughly tied with the Honda Odyssey in overall interior volume.
The size translates directly into lots of room for all three rows of seats. The front seats offer plenty of room in all directions, but the second row takes things a step further. The standard bench is fine, and slides on a track to make limo-like leg room available when needed. It comes into its own when the bench is swapped out for a pair of captain's chairs that offer airline-style first-class accommodations; they have leg-cushion extenders and footrests that give new status to backseat drivers.
It's possible to remove the second-row seats, but the Sienna is a reskin of the former model, and it wasn't designed to allow the middle seats to stow away in the floor--a nifty trick formerly available on the Nissan Quest, and still offered in the utility champions, the Chrysler minivans. The Chrysler way is a better way, though Toyota responds that fold-away second-row seats aren't as comfortable as their chairs.The third-row seat actually has adult-sized room in all directions. It isn't that difficult to enter-and they fold almost flat into a deep well in the cargo area. With the second-row seats moved as far front as possible, the 2011 Sienna has 117.8 cubic feet of cargo room; with the second row removed and the third row folded, it will hold 150 cubic feet of cargo. Even behind the upright third-row seat, there's 39.1 cubic feet of space, almost twice as much storage room as the 2010 Ford Taurus' trunk. The Sienna also can carry an actual 4x8 sheet of plywood.
There's also plenty of small-item storage inside in the Sienna's console, twin gloveboxes, map and side pockets, and available cargo organizer.
The revamped interior suffers a bit in richness; interior materials and appointments feel a bit less refined compared to those of its competitors, in particular the horizontal grain on the dash and door caps. You won't open a vein, but you will notice a difference if you compare it to Aunt Barb's '96 Camry.