Over the years, I've done thousands of these. Yes, thousands. I'm afraid to actually do a tally. Because I just added another 210. Why? Because I wanted to see how fast I could solve them. Plus, I was multi-tasking while watching tv.
The graphics on Filling could be a lot better. In terms of difficulty, they're somewhat challenging. However, where the path must end is almost always too obvious.
Block Path - essentially the same thing
Snake Walk - essentially the same thing
Mortal Coil - this is a much better version. For a variety of reasons.
Stroke! - this version is similar but adds a color matching scheme that makes it devilishly hard.
Full House Touch Basically the same thing but with arrows on the squares.