Are you over her yet?
You've managed to do what every dumped male writer has dreamed of doing: You've written the story of the crazy bitch who broke your heart... and published it! Now everyone will know how cold-hearted and evil she truly is! I can hear your deep bellowing laughs of justice now.
Unfortunately, it's quite obvious that you never took the time to fully understand Summer's real-life counterpart, because the film never develops her character beyond the empty shell-of-a-human-being she obviously had to be to dump a catch like you. You appreciated her beauty, you liked the same things she liked, but you never got to know the girl the way you thought you did. Rookie mistake, buddy. And this is the major problem with your screenplay.
The story starts off strong: guy meets girl, decides she's the love of his life even though she has no idea yet, and attempts to impress her with his karaoke skills. Every epic love story starts this way, sometimes with minor changes, but the karaoke is always essential. So begins a barrage of cute scenes in which the main characters fall deeper and deeper into the treacherous fury of love. They play house in IKEA, tell each other pseudo-important tales of their hopes and dreams, and at one point Tom even prances happily through the streets accompanied by an animated bird (Did this happen in real life too, or did you make it up?). These scenes worked well; props to you! Everyone likes funny and adorable, even bitter, self-important film enthusiasts like myself.
Then, without warning (aside from the post-modern time jumping that has already alluded to this event), Summer dumps you. I'm just going to refer to the main character as "you" from now on, since we all know who Tom really is. Maybe this is how it ended in real life --I suppose that's some kind of an excuse--but it does not work in the film.
You never show the conflict. Your relationship never deteriorates, it just suddenly ends. Even if you found no evidence of your relationship slipping away, there had to be something somewhere that made Summer think, "This just isn't working." And you needed to put that in the script. Maybe she was upset that you got in that bar fight (You macho man, you.), but that wasn't enough. She just disappears for a while leaving us to deal with your moping.
But hey, it's not all bad. Walking into the theater, I was all ready to hate 500 Days of Summer, and I like, totally didn't! I was so worried that this was going to be fantastically quirky and chock full of indie culture that after I saw the trailer, I immediately picked up my hamburger phone, dialed a friend and said, "This "Summer" movie looks like it's going to be totally hip and trendy!"
Thankfully, Summer didn't turn out to be an older, she-wolf version of Juno. The cultural references were relatively tame. Yeah, the Smith's played nonstop, but I didn't have a problem with it. The Bergman parody was even impressive until you showed the chess board, causing the seventeen-year-old film buffs behind me to point out the Seventh Seal reference to their girlfriends. I shook my head at them, but then was equally disappointed that the cliche of Death and chess boards still goes over some people's heads.
So Scott, despite my complaints, I think you turned out something that's definitely worth seeing. It may not be the greatest movie of the Summer ( points for the pun?), but it is certainly a whole lot better than the last screenplay I wrote after being dumped; which was essentially 90 pages of binge drinking and chain smoking loosely tied around a narrative of woman-hating.
This is slightly more mature than that.
P.S. I can't decide if the "Autumn" joke was funny or pathetic. I'll let it slide.