After exactly one game of Hierarchy w/ solo Emissary expansion I think it feels quite similar to Food Chain Island. The process is different, but in both games you win by achieving a valid numeric-ish sequence of all the main cards, each of which has some kind of unique ability which affects the basic rules when you use it, and you have a random side-selection of extra cards (“Edicts”) which are something like a combination of the friendly waters and tough skies cards of FCI (they each have their own unique ability which you can employ one time at any point of the game and, depending on difficulty, you must use a certain number of them).
The set-up (with the deck split into two alternating hands of cards) is more complex than FCI, and the game doesn’t have the spatial element and perfect information of FCI (rather than your moves being restricted by card adjacency, this game limits your moves by only having three cards in each of the hands at a time), but the end result and planning feels similar to me.
There are similarities with Elevenses For One as well, which is an even tinier card game about putting a random arrangement of eleven cards into order whilst navigating the unique rules of each one. I guess I quite enjoy this style of puzzle. (My main reason for picking up a bunch of these Wallet Games was because I was permanently carrying EFO in my jacket pocket, and having additional similarly-portable options appealed to me.)
Hierarchy isn’t a dedicated solo game, and you have to read the regular rules as well as the solo rules, so I feel that I was up and running with those other games more quickly than I was with this one; but that’s just relative – as with all the wallet games, it’s a lightweight rule set, and pretty straightforward once you start playing. Tom didn’t particularly like this as a two-player game, but the card design issue he was most vocal about isn’t such a factor in the solo game (the writing remains small, but nothing is ever upside down); and as something to puzzle your way through without having to worry about how long your turn is taking, I think this kind of game works well.