I loved Synecdoche, New York, but that's not really surprising by now. Every Charlie Kaufman-written movie (besides Confessions Of A Dangerous Mind) has been increasingly more elaborate and affecting than that which came before it, and this, for all its trickiness, ends up being pretty devastating. I have no insights to it that wouldn't be better off if you had them instead. Really great, very dark, brutally so, and after only a short while I was the only person laughing.
My single complaint is the score, which in trying to emotionally engage, only distracts: The other aspects of the movie's artifice are more integrated, this is plainly a convention that could've been done without. It's by Jon Brion, but it's not as unconventional as his good scores tend to be. It's sap, and most of the time it just serves to obscure dialogue.