Really loved the game, I've played just about every other Wadjet Eye game (save for Primordia, which is further down the line and newest Blackwell) and Resonance was a clear winner. I'd even say it can stand proud when compared to better LucasArts/Sierra games.
Proper puzzles with multiple solutions plus mostly optional logic/Mystlike puzzles, intriguing (if a bit underused) conversation system, well thought out achievements, interesting story with a plot twist that I generally did not expect.
Lovely, albeit low-res artwork as well, although I must say I preferred jazzy music from later Blackwell games. Voice over using standard Wadjet actors (heck, Abe Goldfarb voiced three characters, which was an overkill IMO) with special guest performance by Bastion's narrator. The commentary mode was also great, had entries from both main designer discussing the actual design process and Gilbert pair commenting on their executive meddling. About 2 hours of additional content, I'd say.
Extremely recommended if you're even remotely interested in point and click adventure games. It's currently priced at $9.99, should be a no-brainer buy whenever it's discounted to $4.99 or less.