Just because GMail is still better than AOL or Hotmail doesn't mean I agree with the direction it (and Google as a whole when related to Google+ is concerned) is going in.
To be clear, I would be fairly optimistic for the "new Inbox" if it weren't for the new GChat interface which worsened my user experience to add a feature, Google+ integration, I don't necessarily want.
The complaints are not about change in general, but about changes that are simultaneously negative and inescapable. If a new version is better, then great -- but if it is worse and you cannot continue to use the old version, you have every right to complain. I avoid being dependent on web apps for this very reason: I like to be able to downgrade when necessary.