It feels like tags and contexts are the wrong way round.

For example, I'd certainly like to tag some projects as work, some as home.
But I can't tag projects, only tasks.

Yet I can assign a context to a project, as well as a task. This seems bizarre. A project is a collection of tasks, a context is somewhere you do a task. Why would a project have a context ?

I have seen people asking in the forum about assigning multiple contexts to a tasks. You've responded (understandably) that this is not what GTD intends by a context. I agree.
But I would very much like to see "nested" contexts. So @Work could include @Computer and @phone. Then I could say "show me all @Work tasks" or I could be more specific and say "show me all @phone tasks".

Finally, the UI seems a bit inconsistent. I can drag a project to a goal but not to a context. Why one and not the other ?

There also seem to be