I've been running in the (near identical) 3010 for a year. Great shoe. Comparible support to the Kayano (which I also owned), but with a lower heel to forefoot ratio. That is, the 30XX feels flatter and more in contact with the road than the Kayano.
My only criticism of the 30XX is that the forefoot cushioning is a tad marginal for me, but you may find it fine. Heel cushioning is lush. It also has a forefoot cradle which helps with my late-stage pronation. I find it a stable, natural feeling shoe - good heel to toe transition - it flows well. In fact, better than the Kayano.
There's a review here:
http://www.runnersworld.com/article/0,7120,s6-240-400--13496-2-1X2X3X4X5-6,00.html
I've not run in the 21XX so can't compare.
Hope that helps.