So far soooooooo good!
Great gym shoe -- I've had them for a few weeks. Other reviews I have seen have indicated that these run a little big. I'd say that's true - by about a half euro-size. I have Muras and Solutions in 42.5. Size 42 Pythons feel about the same on break in as the 42.5 Muras did - maybe a little tighter (the Solutions were brutal to break in). By the way, my street shoes are about US 12 - euro: 45.5-46.5.
Build quality and materials all seem good.
They're sort of like a softer version of Solutions with proper sticky rubber over the heel. Or a slipper version of the Mura - with a little velcro (and, again, softer than Muras).
It's hard to imagine being disappointed with this shoe if you have liked other La Sportiva shoes.