Nice little cardgame. One Suggestion: After browsing the top left cards the player is losing when turning the last card. I would have won with that card, so it would be nice if you don't lose when clicking on the last card but clicking on the card with the blue plus. ;)
This is pretty challenging, in a good way. Like Solitaire, it's only very rarely that you actually win if you play correctly. The only thing that actually bugged me was that even with the instructions provided, it's difficult to know what you're doing. Maybe a short animated clip would be beneficial, even if it's just as simple as showing clicking on a card, then clicking on it's counterpart to add up to 13 and it going to the pile.
Other than that, great game! And great music too, it's rather elegant and calming.
i...... don't know how to play pyramid....... sorry.