In a real jigsaw puzzle, or in the most serious games in the Apple Store, a puzzle isn’t just a matter of where does a piece looks like it fits: It’s about whether the same of two pieces physically connects correctly. This is extra special in areas with minimal color and shape gradients: There might be 80 candidates that have a similar color, but the edges of the wrong pieces don’t even look like they connect if you look close, as the shape is wrong. A good puzzle solver can then, just by eye, know how pieces pair up without actually looking at the picture.
In this game, this isn’t true. There are basically 4 piece shapes, and the edges are indistinguishable at playable zoom levels. Therefore there is a lot more trial and error in, say, a 500+ puzzle with a blue sky covering 25% of it, when in other apps, or a quality physical puzzle, this wouldn’t happen. So really, this game is jus not at its best past, say, 100 pieces, and you have to go all by the picture.