I'm in the same situation as OP, with a 2008 Odyssey that I've been satisfied with and happy enough to keep driving until now. I've been watching the market for the past few years and took a long hard look at both the Chrysler Pacifica and new Honda Odyssey. Neither of them really did it for me. The new Sienna is not perfect either, but it has enough good things going for it that I just took the plunge and signed a deal for a XSE FWD.
Compared to the 2008 Odyssey, total HP is almost exactly the same but the power delivery on the new Sienna is very different (much better)! It feels very responsive from a dead stop and also at speed, which is nice. I like not having a conventional automatic transmission, which can be a problem area and which might not always choose the right gear. I'm also looking forward to the fuel economy, which will be about twice what I'm getting in city driving and a good bit better on the highway too. I also like the exterior design, especially the XSE trim!