Walker and Silhouette used to be antagonists. He's a police detective; she's a criminal of sorts, though it seems that most of her crimes were expressions of social subversiveness, rather than anything too hard-core. Now, of course, they solve crimes.
Walker & Silhouette is designed to be friendly to novice players, and in particular to get around some of the challenges of parser-based IF: instead of requiring the player to type full commands, it provides keywords that can be typed in or (on interpreters that support hyperlinks) just clicked on. Selecting a keyword means having the protagonist do whatever he (or she -- you play both characters during the game) thinks is the most reasonable action applying to that object at the moment.
Most objects don't get picked up, either, which means that the player has a fairly static inventory. And movement is limited to using the leave keyword when it becomes available -- which means that there's no map to keep track of and no compass directions to memorize. There are even some achievements to unlock, which is cute, a borrowing of game tropes decidedly alien to standard IF.
As one might expect, the keyword-dependency narrows the puzzle range of Walker & Silhouette: any given thing is only useful in one way at one time. It's not completely without challenge, though. It soon becomes evident that puzzle solutions are about interacting with objects in the right order, or timed to coincide right with external events.
I'm describing this keyword-based IF as though it were a novelty. It isn't: people have been playing with variations on this idea for a long time, because it offers obvious advantages to players who find the regular IF parser too frustrating or challenging to learn. Adventures of Helpfulman used clickable keyword-driven conversation back in 1999; in 2007, Ferrous Ring explored the possibility of giving the player multiple modes of play, ranging from the standard parser through keyword play to a system that would more or less play the game for you, so you could read it like a book. There are others. But unless you've followed the IF community and its competitions very closely, you probably haven't heard of those games, and that's largely because they didn't entirely work. Some of that has to do with writing (Ferrous Ring was deeply surreal, so it was hard to figure out what was going on), but some of it was because the authors hadn't given enough thought to how a keyword-based system might be fundamentally different to interact with from a parsed-command system.
More recently, Blue Lacuna offered a partially keyword-based system: it was possible to play quite a lot of the game typing only one-word commands to examine things or move from place to place, resorting to the fuller commands at the parser only for extraordinary actions. But it tended more or less to fall back on the parser when puzzle content was needed; whereas Walker & Silhouette really commits to the idea that the keywords are going to suffice for all gameplay. And they do.
In spite of that, W&S is not quite the same as a hypertext story, and not just because the world model has more state than the average hypertext story tracks. There is still a command prompt, and if you want to, you can type commands in classic IF style. It's not necessary to do that in order to win, and most of the time it won't be productive of anything important, but there are occasionally moments when I wanted to toy with the characters by suggesting actions that they aren't consciously considering. And this paid off: the game responded as though the protagonist was surprised by an unanticipated nudge from the id, often with rather entertaining text.
All this about interface and I haven't talked about the content. Walker & Silhouette is pleasing for some of the same reasons that Gun Mute is pleasing. Pacian likes to take a setting that you think you understand (the old west, early 20th-century England) and then add layers of worldbuilding that make that setting strange and new again. Each new scene brings twists not only for the mystery in the foreground, the one the protagonists are trying to solve, but for the mystery in the background about what kind of a world this is.
I am not describing the setting at all, because one of the constant pleasures of the game, for me, was in discovering that this world contained Surprising Element X... and that Walker and Silhouette considered Element X commonplace. The keyword system helps out with that effect, too, because it allows the protagonists to act on their world knowledge in situations where the player might not completely understand what's going on. If that sounds like a demerit, trust me: in this game it generally works.
Add to that a light romance and a theme about promoting gender equality, and you have a distinctively Pacian-esque piece. It's fun, adventurous, and not too hard; it feels like enjoyable fluff while you're playing, but after you're done you may find it leaves more of an impression than you expected.