I don't think that it should have been marketed or seen as "the email killer" or as an replacement for email at all. Conceiving and positioning it as an enhancement to email and IM would hav been the better move.

You're right, the unification of communication and integration of documents, etc. is a great feature, but for me it lacked of real integration with email and IM. E.g. Why couldn't I get notifications for my Gmail or Google Talk accounts. Why couldn't I push content (mails/messages/attachments) from my mail and IM accounts to Wave directly. So, you're right again, Google messed up the execution.