While the art and the plot are solid. I can't help but feel this story kind of 'soulless', like it doesn't go anywhere and the characters themselves seem like shadows of their former selves at the end. Is really weird.

The author did mention that he was mainly using this story as a way to work out how he himself felt about Sakuya becoming a vampire, so the sense that it doesn't go anywhere might just be a result of that.

I do think the end is well-written, though. Sakuya's lifelessness and Marisa's unchanging nature (I thought it was a nice touch how the stuff she mentioned in the first doujin was carried on here) contrast very obviously with Reimu's awareness of the transience, and thus the beauty, of each day.

For the record, the other two 'Vampire Sakuya' doujins previously uploaded here are actually a sequel to these two stories:
http://dynasty-scans.com/chapters/maid_and_the_bloody_clock_of_fate_lunatic
http://dynasty-scans.com/chapters/luna_dial_maid_to_chi_no_unmei_dokei_lunaticalpha

I'm in agreement that the series is rather well written. The exploration of the various implications/possibilities of Sakuya (and Marisa, Reimu etc.) surpassing her humanity are all rather interesting. The last story leaves off with Meiling also progressing into vampirehood under Sakuya (with the attendant implications of her martial arts skills joined with vampire strength), and Sakuya gradually growing independent of Remilia. Seemed like the series could have had the makings of a compelling action/drama series to me.

I'd also say 'I'm a Gate Guard' should be read before the 'Maid'-series as it is the first mention of the conflict around Sakuya being human (through Meiling's point of view/sentiments).