FS is super simple, embarrassingly cute, a little clumsy, but super addictive...
The basic game is... uh... basic: You're given a spread of cards with some face up and some face down, and you have a deck to draw one card from at a time. When you draw a card, you may then remove a card one up or one down from any face-up exposed cards in the deal. For example, if you have an 8, you can then remove a 7 or a 9 from the dealt cards. If you remove a 7, then 7 is your current card and you can then remove a 6 or a 5, and so on. If your current card doesn't allow you to remove any more from the deal, you must pull another from the deck. When either you remove all the cards in the deal, or run out of cards in the deck, the level ends. Each level is basically identical, with a few small tweaks to the rules (locked cards, mostly, that you must free through various means). Oh, and the cards have suits, but they don't mean anything... you can match suits at will.
There's a story mode that ties a bunch of different groups of levels together, and introduces gameplay modes. At the end of each collection of levels you free a trapped faerie to move the story along. Also, you earn money to buy faerie structures (!?!?!?) that help the gameplay (e.g. peeking at overturned cards, giving bigger bonuses, etc). Lastly, you can find "eggs" that hatch into cute little monsters, which then earn experience as you play and "evolve". What do they do for you? Uhhh... nothing... it just adds ... uhhh.... "cute"...
OK, so a rather limited and extremely easy solitaire game filled with slightly useless powerups, cute little monsters, collecting money (why do we get money for saving faeries?), and uhhh... yeah. (Dear Subsoap -- make these other touches mean something to the gameplay, and you may well be on to something!)
All told, though... it's very addictive! When it's on sale on Steam for $2.50 like it was over the holidays, it's actually well worth the buy if you like easy, quick, fun, casual games.