The biggest challenge with this concept is to create two characters that are repellent to each other, but not the audience. The fact is, neither of them are very appealing to be around, and while we're not supposed to want them to be together, it's hard to believe they deserve anyone else.
The film does have it's fair share of big laughs, thanks mainly to some well written peripheral characters - Stephen Merchant is a particular stand-out. Often though it feels like the quick laughs are at the expense of the story. If situations were more grounded in reality there'd be a greater sense of believability and more at stake emotionally. As it is, you're more likely to have some good laughs, and not care what happens next.
While the main objective is that Rafe Spall and Rose Byrne don't have any screen chemistry (they're actually pretty good together), it's a considerable flaw that their respective love interests, Anna Faris and Simon Baker, are so completely undesirable.
Even less appealing are the wall to wall karaoke covers on the soundtrack. It makes the film feel cheap.
I Give it a Year offers instant comedic gratification, but like the pairing at the film's centre, it just doesn't mesh. I give it a B-.