That's the basic set up, which is conventional enough, but what is intriguing is every decision Liam makes throughout the rest of the movie. He's impulsive, impetuous, and relies solely on Al Pacino/Scarface type gut instincts. Even though he intellectualizes throughout the film, it's as if he doesn't trust himself nor his conclusions.
For example, there's a scene towards the beginning where he's drinking with a buddy of his. His buddy points out a cute girl at the bar, and Liam completely blasts her, calling her fake. Then at last call, when he's lost his buzz and the emptiness and loneliness of life has crept in, he starts to talk to this girl, whom he takes home. Later, she's lying next to him, making small talk and a tear runs down his face. It seemed shocking to me at first, but after a moment I knew exactly why he has crying. The scene was handled very delicately and very few actors could've pulled it off. This is such an interesting character that you can watch him eat a meal for an hour and not get bored.
Hayden is cute and charming. Her character is a dichotomy of maturity and playfulness, often at the same time. There's a scene at the end with her that's almost heartbreaking. J D Moore is hilarious as a writer who's fascinated by the opposite sex. I guess the weak link here is Kelly Hu, who's perfectly satisfactory, but her performance lacks depth. Also, her Chinese accent seemed to go in and out at times.
The best part of the film is the dialogue, which I guess is the thing that made me compare this to Woody Allen.
The movie is not without flaws. As mentioned: Kelly Hu's performance, the subplot with Byron Mann's character at the end (I won't spoil it) seemed contrived, some stilted dialogue by the river (or where ever they were), the scene where they first meet is slightly unbelievable (Beverly Hills teenager taking the bus?) although their relationship was developed well.
I'd say this is love or hate type movie. You will love it if you liked: Lost in Translation, Garden State, old Woody flicks, Little Miss Sunshine and other quirky indie comedies like that. Few things in the plot may not be believable for some, but I doubt anyone would say this isn't entertaining.