Got the game because I was frustrated with a different game that advertised a math crossword feature, but only had one level. Overall, I gotta say I'm not disappointed. The tutorials are fairly self-explanatory, and there's a toggle for if you want errors to show up or not (though the errors go only as far as incorrect math; it's possible to do a problem correctly, but not have the proper components, which can mess up nearby parts of the puzzles, so be careful). Ads are fairly abundant, at a rate of about one per minute of gameplay. Annoying if you hate ads, but ads won't interrupt your puzzles, can be skipped after 5-15 seconds, and if you're quick you can do two or three levels before seeing one. Higher difficulty puzzles aren't hard per se, but they do often require thinking a few moves ahead, so that's fantastic if you prefer slightly harder math apps.
I only have a couple of suggestions/complaints. Like I touched on before, it can be a bit frustrating to do math correctly, but not have it be the right numbers, and the game will mark it as correct (for example, doing "1" + "9" = 10 when the game wants "4" + "6" = 10). Incorrect math shows up red while correct answers are blue/green. It would be nice to have another color, such as yellow, that basically said "you did your math right, but the numbers are wrong."
My last nitpick is that, every once in a while, a puzzle will crop up with an extra number. This makes the level unsolvable, as there's no way to get rid of excess numbers. If this happens during an event, you're locked out of progressing past the painting. It doesn't happen often, but it's just enough to be obnoxious.
Overall though, a really solid math game. Makes for a pretty good time killer and gets you thinking a little bit.