Well, I'll preface this by saying I've not had much chance to actually write code yet despite having the dev preview tools installed, so this is mostly based on just general use of the OS and watching as many of the sessions as I can fit in.

WinRT itself is undoubtedly the right strategy going forward. In many ways it fulfils the .NET promise of giving Windows a much simpler and more modern API interface, without compromising what can be achieved. Many of the other concepts that are being embraced here such as contracts, system managed application lifecycle, sandboxing, asynchrony and task rather than thread focused multitasking are going to really help produce better applications. I really hope these will be extended into the desktop space in future, although I can see how that presents some difficult challenges.

As far as the Metro user interface goes, it's exceptionally good and capable of a lot more than I think some people are currently giving it credit for. It does still need work on defining the "language" for mouse/keyboard use as they are still a bit clunky in places where they don't really need to be. Having to use a scrollbar on the start screen, rather than treating the entire tile area as a dragable entity feels unnatural, for example. Refining the experience in Portrait mode displays would also be a good idea. Whilst it's not common to see ordinary monitor in portrait, it's super handy when reading documents and web pages on a tablet (as a tablet user since the days of XP Tablet Edition it's always been my preferred reading mode). App switching via ALT-TAB also needs work as it's currently a bit unpredictable, due to the way Metro apps are lifecycled.

There are some areas that I think need some refining. Notably the way WNS expires URI's for applications that haven't been run for 30 days, the official response seeming to be don't create tiles that will stop users wanting to run the full app. To me that seems to work against the benefit of Live Tiles and I'm sure there must be a cleaner way of accomplishing this without the WNS service being flooded with notifications for apps no longer in use.