Love the focused inbox, swipe features and calendar integration within the app. The watch integration is as good as any, with ability to view a large preview, or whole message, as well as archive, delete or reply from the watch. If you load your inbox or the full text of a large message, rather than just work with the alert its pretty slow, but that strikes me as the watchs problem, more than the apps.
Snowd0n Peak about Microsoft Outlook