If you don't have plans to see this movie, you can check the spoilers here and then come back.
This was another one of those movies I found myself really connecting with on a personal experience level, so I ended up writing a bit more than usual.
What a deceptive little movie this is: from the first scene it totally tries to win you over with its cute little home movies, its endearingly witty leads and its wonderful soundtrack, but then somewhere around the 45 minute mark you realize all those narrative and flash-forward portents of doom weren't just the usual empty romantic comedy teases, this is indeed about a very REAL relationship, not a fairy tale, and you get gut-punched watching the couple you just fell in love with have to deal with the same stuff you probably did as you were searching for your soulmate and wondering why it didn't always work out like it did in the movies. It's the fact that the second part of the movie is just as powerful and emotional as the first half is charming that elevates it high above the tired romcom genre and into the realm of really good fucking flick. I was concerned going in that the whole non-linear "telling the story out of order" thing was going to be a problem, but it was not at all overused and when employed done extremely well; they did a great job of keeping the scenes set down the line ambiguous enough that it was tough to predict with absolute certainty where things were headed, but so very enticing.
A lot of my friends have been touting Joseph Gordon-Levitt for years, but I've not seen the big deal until this movie. For the most part, he is incredibly earnest and quite self-aware, really nailing that balance of awkwardness and ecstasy of a young man who thinks he has found his end-all, be-all love. I do think he still tries too hard sometimes, overdoing it a bit when he plays angry and forcing a few too many smiles, but he is generally quite giving of himself and it shines through. Zooey Deschanel besides having such a rad look is so good at really inhabiting her character to the point where so much of what she does well is so subtle; she's playing somebody incredibly complex here but never makes her seem unbelievable. She is also so seemless in swinging Summer from enchanting to unbearable as Levitt's feelings towards her shift. There are some real scene-stealers in the supporting cast as well, particularly in Chloe Moretz as Levitt's wise-beyond-her years kid sister and Geoffrey Arend and Matthew Gray Gubler as his two goofball friends; Clark Gregg is a total emerging guilty pleasure for me and I dug him as Levitt's sappy boss.
This was a movie that did funny and heartbreaking equally well and I give director Marc Webb and his writers a heaping helping of credit for creating a beautiful story and then executing it with tremendous creativity. It definitely resonated with me at the same time it was entertaining me.