We bought this 2004 model in the summer of 2003 and now have 123K miles on it. Nearly flawless reliability with very minimal maintenance and repairs. The only issue we've run into has been the fairly common power door cable break. We had a lot of warning (noises, clunky operation) and had it inspected and were told it would cost $1600 to fix. We let it go and now the door is manual operation only. No big deal, we got over 10 years of use out of it while the kids were young. Other than this we've changed the timing belt, spark plugs, and front brake pads (@50K and @100K) plus the usual maintenance items such as oil, filters and tires. Each set of tires has gone between 32K and 38K miles.
Comfortable seats, I can drive 10 hrs without feeling tired. Great visibility. Smooth ride. Interior space, hauling capacity (interior, exterior). Quietness. Just the overall excellent ride that allows for enjoyable car trips. So much better than cramped little sedans, even full-size cars are no match for this minivan in terms of comfort.
I'd love to get better gas mileage. We get 20 mpg combined and our driving is more city than hwy. We used to get 26 mpg hwy (long trips) but in the past few years it's been closer to 24 mpg. With a van this size/weight you can't expect much more. New models are getting about the same so there hasn't been much improvement in 10+ years. I'd like to see a Hybrid Sienna!
I wrote up the replacement of the sliding door cables on my blog and found the part new on ebay for $350: http://johnfixesstuff.blogspot.com/2014/01/how-to-replace-the-power-sliding-door-cables-2004-207-toyota-sienna-xle.html