Project report that returns projects that have only the last task as active, and the remaining tasks completed?

You can do this with Exists statements, but the best first step is to do this as a task report as that will help you figure out what your key details are that correctly isolate these projects.

Is there a reason this needs to become a project report? You can easily list project information on a task report. 

Once you have a functional task filter and a good reason to keep this at the project level, convert your filter to a text mode and copy it here or send it to me personally and I can show you how to make it into a project level exists.

Sorry--I skipped over that you were wanting a project report.

Assuming that your workflow is structured so that the last task can only begin once the other tasks are complete, you could try something like this:

For that task number=total task count filter, you can add this in text mode (you should be able to switch back to standard mode afterwards, unless you've got any other filter statements that can only be built in text mode):