Devoured it tonight, and will likely watch again this week. (almost unprecedented)
The movie plays all around the very essence of memories/perception (the multiple drafts model of consciousness, esp.), and does that & much else subtly & novelly. Its story is always, constantly, the central poignant romance. Insanely efficient, not a frame wasted.
Even better than Eternal Sunshine. Comparable to Before Sunrise...it's actually one possible future several years past Before Sunset.