The extensive FAQ indicates much care, thought, research and testing devoted to making modern improvements and expanding the game while remaining faithful to the original lineage of the most popular mainline versions. Particularly interesting to me were: improvements to the parser, extended vocabulary, expanded descriptions and some careful pruning of a few minor locales which confused many players, never had an apparent purpose and were perhaps never completed in original versions. ADV770 is playable in browsers and currently supported, with the author even offering free individualized, contextual hints via email for stuck players.
Having started with a 4K 8-bit microcomputer, I never got to play the mainframe-based original and have had it on my list for a while. My first experiences with text adventure games were cassette tape-based games written in 8-bit assembler by solo programmer, garage-based "game publishers" and sold by mail in the back of early 80s hobby zines. While those authors were clearly inspired by playing the OG Adventure, the limitations of CPU, memory and only a few months of part-time development by a single programmer clearly showed. The extremely limited vocabulary, abbreviated descriptions and simplified parsers were frustrating, so I suspect I never got the full experience of the larger, more mature mainframe-based games which had benefited from iteration by multiple authors and direct feedback from hundreds of players in university computer labs. I think ADV770 sounds like what I'm looking for: a well-curated synthesis of the most beloved and iconic versions that remains faithful to the OG story and experience but with some of the rough edges fixed.