Update: played a little bit. Some of my statements can be taken critically, but, overall, I like it. Puzzles have initial piece numbers set - a potential "optimum" expressed below and to the right of the puzzle. If you choose to change the number you click on the "scissors" icon that shows the word bubble "modify" when you mouse over it. It does not start out at the default level, but at 12 pieces and you go up from there. One thing different from some puzzles is that the pieces don't snap into the corners, but only into each other. This is by design, since the border size is fixed and generic, so doesn't really match to puzzles, anyway. There is a button under options which says "fasten the pieces on the table" but can't see any evidence of what it does.
I did four 12 piece puzzles, and, oddly, none of the pieces required rotation. But, I started a 100 piece puzzle and piece rotation sometimes seems to be necessary.

To reduce clutter, there's a "pocket" in the upper left corner where you can place pieces to declutter somewhat, and clicking it expands the pocket so you can see and drag back out what you want at any given time. There is also a sort button and a border button - to seperate the border pieces out - and other somewhat standard things like an image button to refresh your memory, or a ghost button to place the image permanently on top of the building area, and a magnifying glass, etc....

Music, which can be turned down to essentially off, is orchestral, and I've only heard one piece so far. I understand that for most people "meditative" music is what you want for concentration, but this is subdued almost to the extreme. But, I usually just turn off most music, so.... In the game folder, in a "Data" folder, the music is in a bulk file without an extension, so I don't know if it can be succesfully replaced or not.

A couple of the 12 piece puzzles glitched on me where 1 piece just refused to move. I suppose I could just move the rest of the pieces to it.... But, I just restarted and it was fine. The credits have Eastern European names, which is fine by me, as I have the same background. I mention it, however, because there's one amusing example of struggling with English. There's a trophy for "inconstancy". I can't imagine they're giving a trophy synonymous with ficklness. I assume they meant constancy - steadfastness. Intially, the trophies are a little silly, because some are awarded for doing just 1 thing, like completing your 1st puzzle. But, after that, the requirement increases by a power of 10 each time, so they become relevant awards quickly. There's also a resolution adjustment under options, but on my monitor it only showed a resolution near, but not equal to, my current monitor settings. Though it was wide screen, though many of the puzzles didn't seem to be wide screen.

As I say, overall, I like it. It is what it says, it basically does what you want/expect it to do. And, the ability to adjust the number of pieces can greatly increase replayability - a big plus for me.

So, thanks again, folks.