I've watched this a long time ago, but I came back to watch it after completing Sweet 18 and I probably enjoyed it less this time though it still has its moments. I do have a few spoilerish parts in Story review below so be warned.

Story (6.0):
It's got all the elements of a fun movie and the setup is okay. There are little parts throughout the film which are fun to watch; however, I couldn't help but gripe at the two main characters. I don't like how they act in the movie and I don't find their connection very convincing.

Let me compare it to Sweet 18 because I think that did a much better job. First off, I know I can't truly compare the two because Sweet 18 got the full 16 episodes to show them fall in love. But it didn't take that long to show it, and it started out with one character already crushing on the other which I thought was a good idea. Here neither particularly likes the other at first, but at least they've known each other their whole lives.

My main gripe was the tension they threw into the movie with dating while married. A similar concept came into play in Sweet 18 but I thought it was handled a lot better. Since the female already liked the male lead in the drama, it was natural for her (especially considering her already developed character traits) to get angry at him for supposed female meet ups and after threatening to go meet guys (to which he replies 'alright!' in a huff) to keep her word and go on a blind date. But that doesn't go very far, and she gets a dressing down from her mother which ends up playing into a major character development arc that she has throughout the drama.
However, in My Little Bride, I couldn't understand the FL. I understand her liking the guy before she got married, and can even condone her playing a little bit with her feelings, but as it went on and her friend kept prodding her how it wasn't right, I just got annoyed with the character and it left little endearment towards her.

Then there's the main guy, who was almost more unlikable in my opinion. He's displayed in the movie as a playboy (and pervert if Bo Eun is to be believed), and there isn't much to convince you he's changed until maybe the very end. Compare this to the traditionally raised and mature lead from Sweet 18 who tells his ex-girlfriend, long before he's in love with his wife I might add, that he doesn't want her to come visit him because his wife wouldn't like it. This is while he is still apparently wrestling with old feelings for that ex. Of course, this lends to less of a potential character development arc for him, but he still gets one and he doesn't get stuck as a jerk in my brain.

Fortunately however, there were a few scenes in the movie with the two getting along and getting to know each other better that didn't make the ending too jarring. I think I'm just having trouble liking it after just finishing Sweet 18.

Acting/Cast (6.5):
I think the hardest part of the cast for me is that I don't like Kim Rae Won a whole lot especially in this role. He's okay 12 years later in Doctors, but I still can't claim I like him. Moon Geun Young on the other hand is not a genius, but I enjoy watching her act. The side cast was okay, but I love her friend Hye Won played by Shin Se Kyung! She didn't have a major major role, but she was the voice of reason when Bo Eun was being stupid, and I love Shin Se Kyung from other dramas (Girl Who Sees Smells).

Music (5.0):
Not distracting or detracting, but not notable or intriguing...

Rewatch Value (6.5):
I've actually watched this twice now, though I skipped the boring parts on the second time through... I don't think I can watch it very often, because I didn't like it the second time through as much as I remembered, but that also might be because I just finished Sweet 18 which I thought did a much better job with a very similar premise.

Overall (6.0):
Maybe someday I'll come back and watch the fun parts again, but actually I'll probably just go watch my favorite parts from Sweet 18. Literally, I don't know how they aren't related, they have so many similarities. Anyway, if you're looking for something cute and a bit mindless, go ahead and treat yourself. I've also just watched Moon Geun Young's Innocent Steps and I'd recommend this story over that one. EH, I didn't intend to write so much about this movie.