Bought my 2005 Sienna as a Toyota Certified Used vehicle in 2008, with 24,000 miles on it. Two wheel drive XLE model with almost every option (leather, DVD, 17" wheel package, dual power doors, sunroof, etc.). The most money I ever paid for a car, and never owned a van before.
Let's start with the bad: Lifetime MPG is 18.6 on the trip computer. This was the last model year for the timing belt - 2006 and beyond have timing chains - so it's a $600 or so proposition every 90K miles for a new belt, water pump, and accessory drive belts. These vans have a very common set of issues, and I've experienced just about all of them: radiator leak, power door latch release failure, leaky transmission pan gasket (not fixed yet, but soon), and wheel hub bearing noise. Radio reception is horrible, as is the ability to see the radio display when the sun's out (i.e. most of the time). The 17" wheels are painted, and the finish must be waxed or it will peel. The transmission must be flushed every two years - regardless of miles driven - if you want it to remain smooth and responsive.
Now, the good: This van does so many things well, and consistently exceeds my expectations. It's been a light duty pickup, a cross-country cruiser, a daily commuter, and a family hauler that my 86 year old mother in law can easily enter and exit. The most practical and useful car I have ever owned, no question. It rides on car tires. The paint quality is fantastic (at least the Silver Shadow Pearl Metallic on my van). The finish has held up amazingly well - and a recent clay bar revealed almost no dirt intrusion, which floored me given its age. The engine is bulletproof. The transmission is good as long as it's flushed often and the pan gasket is monitored for leaks. All interior materials are holding up beautifully after 10 years & 100K miles.