What makes or breaks a mystery title for me and many others is the investigation. One can craft the most intricate mysteries with clever plot twists, but if you aren't able to make the investigation interesting, you aren't really playing on the mysteriousness of mysteries. You're just making a puzzle for yourself.
Toby's Nose seems to get this. You're a dog, so you have to smell everything. Each scent leads to another scent, but they act more like impressions of other rooms. You have to read carefully and think about what might be important to sniff about. It's not just a gimmick, it's a proper investigation methodology where you learn so much about characters' backgrounds and where they've been.
This also leads to some interesting stream-of-consciousness narration. While the title likes to delve into mostly period accurate linguistic fancies, you are never too detached from the perspective of a dog. Your narration reflects a dog living in those Victorian times: the "worlds" these scents conjure are still spaces that dogs (and not humans) would particularly notice. So much of the sensual description revolves around smell, which shouldn't be surprising, but it is still impressive how much the title lands this aspect. You really do feel like you're a dog detective.
I also quite enjoy how you're supposed to "solve" the mystery too. You are supposed to explore all the scents to your content (more likely scenario: as much as you could) and then figure out what actually happened by barking at them. If you're not savescumming and you're indeed thinking things through, the game doesn't really hold your hand. You need to go over the clues, think about how they are connected to the case, and then finally bark them. It makes nabbing the culprit so satisfying because the clues are just waiting to be connected and there's no gimmick or theatrics with it. It's just you and the clues.
All in all, I find this to be a compelling mystery with a really interesting way to do investigation. It's short enough that it doesn't wear its welcome and the game pushes this idea to its limits. I personally find it thrilling to discover new clues through smell. Every new clue strikes me with awe and wonder and I feel I was being rewarded for careful "smelling". Any mystery that makes investigations exciting is always worth commending about.