Decent space for family of 6. Nice interior, comfortable seats. Exc sound sys (prem.). So-so heat in MN winter. Good AC. Gets 26 mpg carrying a full load on hwy. The only problem is that the driver's mirror has become balky. NO other problems. Best reliability of anything we've owned. Nothing rattles or squeaks. I bought it primarily for the power. I was stunned at how quick the Sienna moved when I test drove it. More understeer than I like but that's FWD for you, replacement tires helped a lot. I'm buying more Toyotas!
Excellent power for a mini-van. Amazingly responsive engine. Great build quality (zero issues) and excellent reliability (one minor problem so far).
Any vehicle could be improved. Make middle/rear seat attachments to the same plan so seating could be rearranged in more ways. Tighter turning radius would help. Economy-mode shifting would probably help city MPG (seems to like lower gears). Rear/side visibility somewhat restricted.