My basic, idiotic take on Mondrian is that he's one of the hardest artists to see. I don't mean that you have to climb a lot of stairs or find your way through a maze. I don't mean that curators like to bombard you with dry ice as you approach. I mean that, once I look at a Mondrian - the classic grid-based Compositions kind of Mondrian - it's always been quite hard for me to really take it in. His squares and lines and blocks of primary colour have been thoroughly co-opted by the advertising and design industries. He belongs to the billboards now. He's on cosmetic bottles and dresses and iPhone cases. He's retro even - not 1930s retro, 1980s retro. (These are possibly all excuses: in reality Mondrian just makes me feel a bit stupid.)
Oh, and he's also the kind of artist that makes a certain kind of person say, "Well, I could've done that. Give me a ruler and a bunch of red and black and blue and yellow paint, and I could knock out Mondrians all day." Look at those elements of the classic Mondrian - again, the grid-based L'Oreal Mondrian that most easily comes to mind. Black lines. Blocks of flat colour. This Mondrian is surely a creature of MS Paint?