Nice one. I'm a bit surprised at the high difficulty rating, I got through this one completely logically in contrast to some of the other most difficult ones. But probably I just missed something there.
Well the solving times do seem to support this, since those seem to make it the hardest of the 4-star puzzles. It's just that I remember fighting very hard with some of the others (maybe http://puzzlepicnic.com/puzzle?1753), but it's likely I just missed something there.