Nothing really. I did have to replace the run-flat tires after 39,400 miles. That's about what I expected. These tires are very expensive; about $1300 for 4 new Bridgestone tires. The very Toyota agency that told me I needed them didn't have them in stock! I went to Direct Tire that very day and had them installed.
If I try to accelerate too fast, the Sienna has an annoying habit of hesitating, then downshifting from 4th gear to 1st gear, which puts a strain on the engine. This problem does not occur if I accelerate gradually.
This is the All-Wheel-Drive (AWD) version which has been great in Massachusetts and when I take winter trips to Maine and New Hampshire.
On dry pavement, the Sienna handles far better than my 1996 Ford Explorer.
The Sienna is roomy, with a firm comfortable ride.
Everything, CD player, radio, air conditioning, power door, power windows, heated mirrors, has worked as it should.
I got a nail in one of the run-flat tires. The low tire pressure light came on. I continued to drive for about 40 miles before taking it to a Toyota dealer. They repaired the tire, and I didn't need to replace the tires til about 39,400 miles.
I've read other comments which complained about having to replace run-flat tires after about 12,000 to 17,000 miles. That just hasn't been my experience.
I check my tire pressure once a week. I also check the alignment and the tire balance whenever I get my oil changed. All of these things affect the rate of wear on the tires.
Sienna is the only minivan that can be ordered with All Wheel Drive. Chrysler no longer offers AWD on their minivans because there's not enough space under the van for a spare tire, fold-away 3d row seats and the AWD. On the AWD models, Sienna does away with the spare tire by using run-flat tires which are designed to run for at least 50 miles with a puncture.
I'd prefer to have a spare tire in addition to the run-flat tires, just in case I'm more that 50 miles from getting a replacement or a repaired tire. Toyota does offer that option, but it means losing the ability to fold flat the 3d row seats.
I'd like to see a spare tire mount on the rear tailgate.
In spite of all that, I must admit that the run-flat technology works well.