Pianist Jeremy Denk, whose blog I've recently started reading, has a deeply moving post about playing Messiaen's Quartet for the End of Time:
It is a piece for the "end of time," and yet the pianist (yours truly) has to be time. In the cello and violin solo movements, I simply play chords, awkwardly slowly, marking moments which are much slower than seconds, and marking (with my harmonies) a larger, really time-free, arc of meaning under the melody. In no other piece do you feel such a tremendous strain between something achingly large (something that only eventually will be expressed) and the snail's steps you must take to express it. But he (Messiaen) manages it; not a note is out of place in the last movement; every harmony is extraordinary, an essential step, a grammatical and striking word of the holy overall sentence... somewhere toward the middle of the last movement, I began to feel the words that Messiaen marks in the part, I began to hear them, feel them as a "mantra": extatique, paradisiaque. And maybe more importantly, I began to have visions while I was playing, snapshots of my own life (such that I had to remind myself to look at the notes, play the notes!): people's eyes, mostly, expressions of love, moments of total and absolute tenderness. (This is sentimental, too personal: I know. How can you write about this piece without becoming over-emotional?) I felt that same sense of outpouring ("pouring over") that comes when you just have to touch someone, when what you feel makes you pour out of your own body, when you are briefly no longer yourself -- and at that moment I was still playing the chords, still somehow playing the damn piano. And each chord is even more beautiful than the last; they are pulsing, hypnotic, reverberant... each chord seemed to pile on something that was already ready to collapse, something too beautiful to be stable... and when your own playing boomerangs on you and begins to "move yourself," to touch you emotionally, you have entered a very dangerous place. Luckily, the piece was almost over... When I got offstage I had to breathe, hold myself in, talk myself down.
Who needs music critics when performers write like that? Read the whole thing here. My own attempt at a panegyric to the Quartet is here. The recording to get is Tashi's. If you have some notion that "great music" ended with Brahms or Mahler, the Quartet is the work that might make you think again.