Who, What, When, and Where
This series takes place in Hong Kong where a group of CIDs work in the Central Hong Kong Police Station.  Tse San is the leader of his unit including Fei in it.  At first Fei was a very cold guy when he first went working with the unit but smart as well.  To be short, it is mostly about the team solving murder cases and also dealing with their love life.  Quin works with the police force as well as a psychologist.  Quin begins to like Fei but Fei still can't seem to move on since his girlfriend, Chin Chin, disappeared for 3 years already.  But later on, Fei finds out that he cares about Quin and wants to be with her.  As
they are together, they constantly fight about Chin Chin, which causes problems between them.  Tse San and Ah Man have been together for a long time.  Ah Man's best friend, Tong Sum secretly likes Tse San.  Ah Man finds out about Tong Sum's feelings for Tse San and thought she wasn't good enough for him so they broke
up.  Ah Man goes to jail (not going to tell why) and pretends that she doesn't care about Tse San anymore so that Tong Sum and Tse San could be together.  Soon Tse San finds he has feelings for Tong Sum as well.  Later on, after Ah Man got out of jail, she spills out how much she still cares about Tse San and wants to get back together.  But Tse San had refused because he doesn't wants to hurt
Tong Sum.  Tong Sum and Tse San got married but sadly Tong Sum got killed accidentally on their wedding day.  Fei and Quin loved each other so much that they planned on getting married.  But a surprise had stop them.  Chin Chin has return after 3 years; she was actually kidnapped by Fei's enemy.  After finding out how much she had sacrificed for him, Quin had to give up her love.

Best Love Triangle
I would have to say that I enjoyed the Quin-Fei-Chin Chin love triangle.  It was more appealing and interesting to see how they always argue about Chin Chin even though she wasn't there.  Also it was nerve wrecking to see that every time Quin and Fei gets a chance to be together, something occurs which causes them to
argue a lot.  Their relationship keeps going back and forth.  They argue and don't speak for a while and then are together again and keeps happening constantly.  The Ah Man-Tse San-Tong Sum love triangle wasn't that interesting to me because maybe Charmaine Sheh's character wasn't that likable.

Likes and Dislikes
I liked how Louis and Sunny's characters was smart and intelligent when they solve cases.  But when it came to their love lives, they where stuck.  Also, I liked how Tse San and Ah Fei's friendship became stronger, helping each other out.

I didn't really enjoy Charmaine's character; it was sort of annoying.  Her character seemed weak and tries acting innocent too much.  If you had watched it, you will see what I mean.

I didn't like Anne't acting as well.  I don't know if it's just me but her
acting sucks.  She always seem to act innocent; not in just this series but others as well.  She didn't seem to put much effort in it compared to other casts.  Even though she was Miss Hong Kong, she needs to work on her acting.

My favorite scenes were all of the times when it had Ah Fei and Quin together. From the tennis scene to the proposal and especially the kisses!  It was very romantic to see them together as a couple.  Not only that, they always have that background music playing which you know is about them two; it was like their own song throughout the series.  When Quin was playing hard-to-get, it was anxious
to see when they will finally be together.  I think that if Quin hadn't been playing games, they would have probably been married already before Chin Chin's reappearance.

Best Chemistry
Of course Jessica and Louis!  Why? It's because they look so cute as a couple together!  Their chemistry seemed so perfect for each other.  But sadly they don't get together in the end.  It's too bad they aren't a real couple in reality. =[

Pity Factor
This series is one of the best detective series I've seen.  The love story was what made it worth watching.  But there were some pity part to it as well.  It was very sad that Tong Sum died on their wedding day leaving Tse San mourning. When you watch his performance towards this, you can feel his pain and sorrow as
well.  It was their chance to be together forever but faith took its turn and killed it.  It was sad to see she got stabbed accidentally by Tse San's sister on her wedding day.

For those who have watched this series, you would agree with me that the ending totally sucks!!  You would have thought from the moment you saw Quin and Fei together, they WOULD be together till the end of the series.  Here's the pity part: they didn't!  It didn't seem right that Ah Fei had to go back to Chin Chin because of  the things she done for him.  You could tell that both Ah Fei and Quin still care about each other a lot, especially the part when Quin return his
key and also the bar scene.  It was heartbreaking to watch the part when they were in the hospital where it was the end for them.  It also pisses you off how they just end it like that.

By the end of the series, it was a pity that both guys didn't get to be with the woman they loved.  Tse San didn't get to be with Tong Sum or Ah Man and Ah Fei didn't get to be with Quin but with Chin Chin instead because he chose responsibility over love.  You will feel pity most for Tse San and Quin.

When watching the scene when Quin returned the key to Ah Fei with their last hug and kiss, it was like why cant they just be together?  Also with the bar scene you can see it in their eyes like when Quin watches Ah Fei walking away, you see that she still truly love him; especially when they were playing the "Big Big World"song.  Also when Ah Fei saw Quin and Tse San talking together, you can
see that he was jealous.  Its so sad it had to end like this for them!

Most Dramatic Scene
There were two: one is when Tong Sum is rushed to the ER.  It was dramatic to find out that she doesn't make it in the end.  While watching the part where Tse San goes to see her for the last time and slips on her wedding ring and kissed her, you begin to feel grief and sad.

Second: it would have to be the scene at the hospital when Ah Fei grabs her and hugs her.  Watching Jessica cry makes you feel upset that they couldn't be together.  It also makes you feel piss as well.  Especially when she walks off and it has the music playing, that was the most dramatic scene between them.

Performances
Sunny Chan, Louis Koo, and Jessica Hester Hsuan did a great performance, carrying out their characters.  What made them good was that they acted with emotion and make it seem so real.  Like when Quin cried at the hospital and Louis too.  It was so real!  Also when Sunny was at the beach with Louis after Tong Sum's death, he did a great job acting the anger and emotions that you feel it as well.  Others, like Charmaine Sheh and Anne Heung still needs improvement. Not only that they gave a terrific performance, Jessica and Louis made such a cute couple together!  I hope to see them more together as a couple in future series; hopefully soon!


Worth Watching?
With its long episodes and murder cases, over all this movie is worth watching. Even though I didn't like the ending to the series, I think that is what made it worth watching.  They always go back and forth and when you finally think they are able to be together, it turns out in the end they don't.  By the way, what is with the last scene, the one in the bar? It was good and all but it felt like there was going to be a continuation to this (DIF5).  But there still isn't one! Everyone would agree with me that there SHOULD be a continuation and watch what
happens next to the characters.  I have read a lot of fanfics which are written by people as a continuation to DIF4 but I wish TVB is actually producing it and finally see that Louis and Jessica are together!  For all Louis and Jessica fans, this is a must watch.  Not only is this a great storyline, Louis looks hot! =D

Rating (scale of 1-5, the higest is 5):5 - Excellent