I'd compare it to one of Araucaria's Bank Holiday specials -- the sort that you might nibble away at over a few days. There are always a few
really obscure words too, but the grid structure means that there are more crossing letters to help work them out. I don't know about you, but I can stare at a crossword for hours and not get a particular word, then come back a bit later and see it straight away without even looking at the clue.