I have just finished watching Part 3.
Part 1 was the best. It was really about vampires; focusing on their lifestyles, struggles, interactions, etc. Though there were some quacky moments (like the last scene where everybody just sat in the bar - a boggling attempt at the abstract), it was generally fresh, well-paced, exciting and built up to a climax. The twist to the plot also had a deep impact to the storyline.
Part 2 is boring and forgettable. The problem started when it introduced the alien concept to the vampires. And what a waste of the acting talent of Simon Yam! It was also uncalled for to cast many of the same actors and actresses from Part 1 as new or similar characters in Part 2. It was not giving any deja-vu effect if that was the intent. It came across as a opera troupe needing to recycle its limited actors and actresses for its next production. The plot was so uninteresting and the ending was so bad (the power of a couple in love holding bow and shooting arrow together to end the threat) that the only good thing I can remember is the theme song.
Part 3 is somewhere in between. The good parts were that the writer has a good ability to weave various subplots together and interlink different elements throughout. It was well thought of. More goofy elements abound (like Fate as a character, and 'gods' and spaceship 'nirvana'). These were outweigh by great new additions, like Ma Siew Ling's family members, her daughter, her buddy from Mo family and the exciting subplot involving the anti-ghost SWAT team. If only these have been better fleshed out. And Mark Cheng's character was certainly more cool than Simon Yam's. Though so, the story was merely a watchable mediocre. The build-up to the climax was a gradual slope. And with the possible worst-case future already revealed, it somehow took the mystery and suspense away. The plot also have us rooting for Tin Yau's Previous Life (Arrow-head) before relegating this character we have built up a bond with to a supporting role. Consequently, one have little opportunity or time to bond with the actual Tin Yau himself as he was introduced later and most of his endearing heroics were in the earlier Part 1 & 2 which were watched a couple of years ago. Then there was the soft-on-the-inside but hard-on-the-outside Siew Ling's character which was unique and iconic. Well, the plot would turn her into a generic plain-jane heroine eventually. In the analysis, this isn't really a series about vampires. With some minimal plot changes, the whole plot would work as well by substituting say, mutants or great pugilists for the vampires. Sigh, I blame it all on the plot. It has all deviated so much from the spirit and energy of Part 1, they may have killed this franchise once for all. The sad thing is that with the strong cast and great production resources, it could have potentially been better than Part 1. I don't suppose there would be a Part 4; or at least not anytime soon.