I've always brushed off "Soulmate" to the side and kept it lying on the shelf for some time because skimming through it, I didn't find it very interesting or appealing.
First impression:
1.Not a very good looking cast - at first.
2.Mature content - It seemed very Amercanized. Nothing wrong with that, but if I wanted to watch something "Americanized" I would have just turned on the TV.
3.The couples didn't seem to fit - No chemistry at all.... in a glance.
BUT after watching the first episode, I was hooked. In one episode, the characters grew on me, it turned out that it wasn't as sexified and thoughtless as I thought it was going to be, and the couples that I thought were the leads were not the.. "Soulmate."
After watching this 24 episode "sitcom" (30 minutes each), I thought it was one of the best Korean romantic-comedy miniseries I've seen.

STORY - Soulmate was basically about 6.. well.. 8 people's love story, presented in a very comical way. Lot's of characters=lot's of side stories. There was pretty much 2 main stories, one with a couple in a relationship of 5 years slowly breaking apart, and another about a couple starting to blossom.
What I really liked about this drama is that the story had what you call DIRECTION. Watching this drama, you could tell that this drama was well planned because of the way the story flowed. No unpleasant surprises or crazy twists that doesn't even flow with the story, but just a nice, well written, well produced, and well acted drama. (A little spoiler) The two leads of this drama actually meets a lot later than usual, yet, it doesn't get boring at all. In fact, it was one of the reason that made this drama so aniticipating.
The comedy in this drama worked well, it had a nice mix of comedy and romance. It was quite mature, but entertaining otherwise.
The only thing I didn't really like about this drama was that it didn't seem to have had enough scenes between the two main leads. They spent too much time building up the side stories, thus not giving enough air time for the two "Soulmates," but I guess it was forgivable.. even though Dong Wook (main guy) and Yujin (support) didn't seem to have any chemistry, they sure gave a lot of laugh.

ACTING - I've already said that it was a well acted drama. I don't understand why these actors aren't the face of the new Korean dramas coming out today. LSK didn't seem "leading lady" material at first, but she definitely proved herself throughout that drama. SDW did a convincing performance. Shin Min-Ae (the hot girl) wasn't believable at all, at first, because I didn't think she had the looks, but her charisma lit up the screen. Together.. Philip, Sa Kang, Ryo, MiJin.. they all really had chemistry.

MUSIC - This drama has one of the best soundtrack in k-drama history. The song selection was very hip, which fits perfectly for this hip, trendy drama.

Overall, I have nothing but praises for this drama. It really surprised me on how good it is, it was definitely unexpected. If you like a good romantic-comedy.. this is definitely a MUST watch.