I saw a talk by professor Max Roberts (who can be found at tube map central) and he’s done a dozen redesigns of the London tube map. Since Beck, the system has got over complicated so that the current official map is too busy and confusing.
One of his principles is that strictly sticking to octolinear lines (horizontal, vertical and two diagonals) isn’t necessarily useful, and you should use the system that works for your map. In London, using a hexalinear system (horizontal, 60 degrees and 120 degrees) means that you greatly reduce the number of curves inside the circle line, which makes the city centre much clearer.
Also, something he said in his talk was that just because you don’t like it, doesn’t mean it isn’t better. In testing, lots of maps work better than the official ones (in the sense that people can find better routes faster) but they will then say they like the old map more.
