From the screenshots it looks very much like a Google app, and probably is pretty smooth. It is closely integrated with Gmail, and it has an events focus which makes it look like Google is going to be getting into events a bit and also some social networking with the sharing of calendars and events. Naturally there is RSS, integration with iCal, and other features.
I’ll just go ahead and say I’m glad I’m not an investor in one of the other new standalone calendar applications like 30Boxes. There’s probably room in the market for one startup in the space for those users who want something totally unique and standalone, but you can be sure both Microsoft and Yahoo will have improved calendars in the near future with tight integration with their email apps and other services. This integration, widespread use, and promotion will make it tough to compete.