I would disagree, I find it a different beast compared to 8. I've been using the technical preview for months and it has been pretty solid. The normal test version mishaps of course but all in all it was smooth sailing, bug fix delivery and new builds were generally good. It is definitely good enough for our internal use and that is also important to help us learn it and fix it. The usual first round of bugs are already appearing as is want to happen when MS release a new OS. I'm encouraging clients not to upgrade yet from existing systems although as our customers buy OEM computers it is going to be forced on at least a few new production systems in the near future.