The short version is that Valentine's Day is a mish-mash of vignettes that doesn't quite work but by the somewhat looser standards of romantic comedies, isn't a bad way to kill two hours.
In recent history, the best example of this type of movie is Love Actually. You have a bunch of beautiful people - some connected, some not - intermixing around a theme that works to its conclusion - happy endings for about 80% of the cast. As a connoisseur of the romantic comedy genre, I can see the attraction of film makers to try this type of story because when it succeeds, it's a work of art. Valentine's Day is a decent try - but it ain't no work of art. Directed by Garry Marshall, the movie meanders all over, making it difficult to get to know the characters, much less like them and root for them.
There are about two dozen characters in Valentine's Day and all the action, naturally, takes place on February 14. Some couples are falling in love, some are breaking up, you get the idea. There are just so many, and so many of them were big stars, it was hard to know who to pay attention to and who was just window dressing. For example, the movie opens on Jessica Alba, but she's only in a few scenes. Another example is Queen Latifah, who makes a diva-sized entrance but is only in three scenes. Three small scenes. I checked my watch - the last major character made her first appearance 32 minutes in. Thirty-two minutes and we're still meeting characters? Of course this thing wasn't going to gel. Alfred Hitchcock once said he liked casting Jimmy Stewart and Cary Grant because he didn't have to waste the first fifteen minutes of the movie on exposition. When you have two dozen characters, they need a little exposition. Marshall went light on it and jumped in to the heart of the stories, and it didn't go well.
Nonetheless, as far as romantic comedies go, I'm going to say to go ahead and rent Valentine's Day. It will get the job done but it's not as good as it should be. And rent, don't buy.
Now that that's out of the way, let's talk pet peeves. In the megastory genre, the stories all have to mesh at the end. To do that in a fun way, you often have characters that are connected but not in each others storylines meet at the very end. It's called a reveal. In Valentine's Day, there are two reveals in a row done the same exact way. It's midnight and one character is sleeping. You see someone enter the room. The view pulls back, you see the other person and there should be a big “Oh” moment. Once is fine. Twice in two scenes is audience abuse. Plus, Marshall tipped his hand with one - the woman who never said who she was traveling to meet never said it just a little too obviously.
Then there's the beautiful people. Why do film makers think we will buy that pretty actors will be unlucky in love? See my review of When in Rome for one example. In Valentine's Day, Jessica Biel - the gorgeous and extremely buff Jessica Biel - plays a woman who is so unlucky in love that she has an unvalentines day party every year. Please. I bought that her character was neurotic but someone who looks like that and has a six-figure job as a PR flack is going to have guys lining up for blocks. In that line will be plenty of frogs but probably a prince or two. Once she accepts her lot in life, she would no doubt develop a jerk radar, and could easily sort through the frogs to find the prince. I, for one, would be in that line, for a chance to be the next ex-husband of Jessica Biel or Kristen Bell (or their characters). I would also be one of the first frogs to get the hook, of course, because that's my lot in life. I'm typecast.