IMHO, Inform6 (which is a true object-oriented programming language) is much more powerful than Inform7. I tried both and found that: I7 is not consistent and often ambiguous: some pieces of code would get broken after inserting a perfectly valid "sentence" with no explanation; compilation is slow, execution is slow; some tiny compiled text games with no picture and no sound weight more than 5Mo. If I had a large project to code, I would take I6 without a doubt.

Everything you said about I7 is true, but its real value comes from the abstractions it introduces.

That is, it isn't just an English-like syntax for writers who are used to writing in complete sentences... it's a programming model based on concepts from narrative, technical writing, and linguistics, for writers who are using it to write narratives, describe technical systems, and manipulate text.

I7 integrates high-level domain concepts of interactive fiction into the language: scenes and continuity, rules and their exceptions, relationships between objects, templates for parsing and printing text.

Inform6 was first, and it was far easier to grasp than ZIL and Inform7 itself.