I left work 4 hours early today to study for a final....I spent 3 of those hours playing Picross. I'd check out your suggestion, but I'm honestly a bit scared.
Be afraid. It is addictive as hell. It gets hard but never unfair (so far). There are many, many puzzles, grouped by temples. At the end of each temple, there's a bonus puzzle which works a bit differently. Whenever you finish a row, it goes away and a new one is added. When you collect enough gems or run out of time, you're done. This is the same premise as the arcade mode. The difference there is that each successive puzzle adds one more row & column. This mode ends after Stage 11, and I'm so glad too. The time left over from each stage is added to the next stage in arcade mode, and it would just get to last too long now that I really understand the Picross logic.
Scoring depends on time, and after puzzles get to a certain size, each successive tile scores higher if they're removed in rapid succession. Scores can vary greatly depending on quick thinking and mouse sweeping. Using the right mouse button for hammering out bad tiles (not in the picture) is not the default. It should be, and must be set under Options. If you hammer a good tile (in the picture), you break a gem. You can make that mistake up to 4 times. The 5th time ends the round (with a loss). Revealing (left-clicking) a bad tile gets you the traditional time penalty. There is no free tile marking of any kind, unlike the Nintendo game I tried.
Nicely done, really. Thank you and curse you for turning me on to this.