Google Wave has been reviewed in multiple places, but mostly by looking at the usefulness of the GUI tool that Google has made available. Instead, this post will focus on it's ability to compete with alternatives.
Google originally launched it as "e-mail as it would have been if we designed it today". However, it actually does not compete well with e-mail, for several reasons:
* There is currently no gateway for e-mail, indicating that it may be a problem to integrate it well with other messaging systems (SMS, MMS, SMTP, etc.)
* It can be very confusing to find out, who wrote what to whom and when. The replay function does not give a quick overview.
* It can be hard to find out, where in a wave there are changes.
There are many more reasons why Google Wave doesn't compete well for mails. It also does not compete well with most IM systems:
* In Google Wave, Person A can add person B to a wave that includes person C.
* The chronology is not 100% clear.
Again, there are more reasons. Google could probably build much of the features of e-mail and IM systems into the Google Wave protocol, like "do not allow participants of this wave to include other participants" etc., but a perfect IM system, built on top of Google Wave, would probably not be much different from other IM systems.
Collaboratively editing a document works much better in Google Spreadsheet than in Google Wave, simply because Google Spreadsheet delivers more structure to the document, with columns, tabs etc. For almost every generic purpose in Google Wave, there is a specialized application that does the job better, and these specialized apps usually work well together in a session.
Gadgets change the game: Gadgets make it possible to do things like collaboratively edit a mind map. This is great stuff, but it could have been done in Google Apps, as a new mindmap tool, too. As long as Google delivers it all, and you need to sign into Google to use it, there is not a huge difference. You can also insert gadgets in collaboratively edited Google Spreadsheet documents, so inserting Gadgets in Google Wave is not a benefit per se.
If an application developer wants to create a gadget for collaboration, this can be done in Google Spreadsheet or Google Wave. In both cases, the gadget needs to be available on a central server. However, there is one big difference: With Google Spreadsheet, data is stored in a single online service, whereas Google Wave makes it possible to have the data available on multiple servers at multiple companies at the same time.
Therefore, we can define Google Wave as: A platform for online collaboration applications, that features decentralized data storage and decentralized user authentication.
Google Wave becomes interesting when one of these events happen:
* the main user interfaces gives easy access to great collaboration gadgets
* companies start adopting Google Wave internally in their organization