This game gives me mixed emotions. The individual solitaires are all so creative and interesting, and each one needs a unique mental approach. Plus the art and music are fantastic. But holy crap the difficulty is *brutal*, and this is coming from an avid Zachtronics-Solitaire fanatic.
Many of the games have hidden the fact that the gamestate is actually unwinnable from many turns ago (usually because there is a limited resource that you unknowingly expended, often ten to twenty real-life minutes ago). Many of them have a severely disproportionate difficulty spike right at the end. I played several games that were tough-but-doable for as much as 45 minutes only to find the endgame mechanics (which I had never reached before) actually start restricting space and it quickly became impossible not to tie myself into a knot.
A detector for games which are already lost would be nice, although I understand that poses a pretty extensive coding challenge. And the same statement applies for an undo button.
Most of all I think the game needs a better way of easing players in, rather than dumping all 23 games in front of them. The star rating system is pretty inconsistent at best, but currently there's no other way for newbies to know where to start. Maybe if games were unlocked in incremental batches? Or if specific games unlocked their shake-up versions like Tap -> Baba and Single -> Binary.
((Also the "playable with a standard deck" notes are greatly appreciated. Very cool.)