I am not a stranger to difficult puzzles; if you check my reviews you'll see I did a 1000 piece puzzle of the Wicked poster, which is entirely solid blocks of color and almost exclusively three colors.  This puzzle, however, is almost as difficult and ten times more frustrating.  The pieces do not fit together cleanly, and sometimes when they do you realize later they weren't supposed to.  I have redone the border multiple times, and have had large sections that I thought was complete only to have to remove pieces and use elsewhere.  The end result is turning out great, but it's taking us much longer to get there than it should.  At several points we're having to turn the puzzle upside down to see if the fit is correct on the back.