I finally managed to see this movie. I figured the combination of the Farelly Brothers (directors), Nick Hornby (who wrote the novel on which this was based), Lowell Ganz (screenwriter), my beloved Boston Red Sox, and a host of decent actors would come up with, well, a better movie than this.
Not that it's awful. Some funny lines are uttered. But I have my doubts whether Jimmy Fallon has the chops to make it as a movie leading man. Drewie Barrymore is also kind of flat. (I thought he was excellent in a small role in Almost Famous.) As a romantic comedy goes, it's utterly predictable. The Fenway scenes (however) are fantastic. However, if you want to see a movie based on a Nick Hornby book, go for High Fidelity.
But it's got JoBeth Williams; I don't think I've seen her in a movie for about twenty years!
Also note that the link above is to the special "Red Sox" edition of the DVD; consensus is that other than the nicer box, the DVD's extras aren't worth the additional price.