Firstly, there seems to be no comparison between an 08 and 09 models, the engine is improved to the point where they could have renamed it. Secondly real world on road handling is superb, if you're coming from a GS gmake sure you have a good long demo, it IS different but within a mornings ride you'll love it for the same reasons you love the GS, predictability and precision. Having said that, a standard Stelvio that I rode seemed to run wide, could have been the set up though.
The engine is a peach, and you've still got the big vibes you get on a Boxer engine...plus a glorious exhaust note.
I've given it 4* for reliability as I just don't no yet but the quality seems excellent, very well put together, but even that depends on your dealer so who knows.