All server-to-server communication is TLS encrypted and authenticated. All wave origins are verified using digital signatures, so, to quote from wikipedia,
Therefore, a downstream wave provider can verify that the wave provider is not spoofing wavelet operations. It should not be able to falsely claim that a wavelet operation originated from a user on another wave provider or that it was originated in a different context.
Thus, spam really ceases to be an issue
DomainKeys does similar things for e-mail.
Waves can be embedded. Blog comment sections can be replaced by waves; forum threads by waves. All comments would appear in your inbox. Email cannot even hope to replicate this other than with the clunky-and-annoying "notify me when someone responds" forum setting.
First, I might not want all this integrated into my e-mail inbox. Second, Facebook (and probably OpenSocial, Google's other thing) does this - integrating forums, discussions, comments, likes into posts, which are arguably wave-like.
You can easily add people to the discussion. The only way to do so with email is to re-forward the whole chain of emails to them and ask them to reply-all; or to include them in the next reply-all and hope that noone else responds first. This is a pretty glaring flaw of email that Wave fixes.
I'll argue it's much easier to scan through an e-mail thread than do a playback on a wave. Real-time playback is cute but I don't have time for it. And reading the wave linearly doesn't help since people can modify things in between.
There are of course a ton of other reasons why Wave was more than just "chat with a couple of features", but these were big. Wave had the chance to completely redo how we communicated, freeing people from having to keep track of 10 different IM networks + email + forums + blog comments.
Google couldn't even integrate GMail with wave. One of the main reasons I gave up Wave was having to keep track of two Google inboxes.
Its a little disheartening to see so many people (even techies) who dismissed it out of hand given how much better it was (with no disadvantages that I can discern).
I don't think people dismissed it out of hand. When it first came out, people lined up for accounts. It just didn't offer anything much in addition to what we had.
Finally, given the above, how can people POSSIBLY be responding "and nothing of value was lost" in an honest to goodness impressive attempt that was completely opened to the public (source for the servers was released!)? Is everyone really that in love with MS Exchange?
Maybe nothing of value was lost precisely because everything has been opened up anyway? Anyone who wants another shot at convincing people that this is a Good Thing(tm), can quite easily do so. I agree that there was phenomenal engineering involved and that may well be used in many scenarios.