Sam Winter gives a short summary/commentary on the decision

The judge seems to be saying this (the main points anyway).

1. Whatever else W has done, she remains genetically male (para 32)

2. The Marriage Ordinance of Hong Kong explicitly refers of men and women marrying each other (and that is its Christian intent) (para109 and elsewhere)
Whatever social changes there may have been, a core feature of marriage remains having children and raising a family. (para 204).

3. The rights to marry in the Basic Law and Bill of Rights (itself based on the ICCPR) are also intended for men and women marrying each other (para 168 and following)

4. For purposes of marriage W should be considered, under the current marriage law, a man (para 121, 162). Her marriage to her boyfriend would be a form of same-sex marriage (para 251)

5. The Court would be going too far in interpreting the current law to allow W to marry a man. Indeed to do so would reconstructing marriage as being beyond a man and woman, and possibly go beyond social consensus (para 190 and following, para 211 and following), and open up a range of broader issues (para 147 and following)

6. Therefore the Government and Hong Kong's Legislative Council would need to change the law before transsexual people could enjoy the rights to marry claimed by W. (para 149 and elsewhere).

The judge's comments on the absence of social consensus is a little ill-informed. He  needs to get out and about a bit more and mix with a broader range of Hong Kong people than he obviously does. My colleague Mark King  did his PhD research on attitudes to transpeople in Hong Kong just a few years ago. His study was a large, randomised sample telephone survey involving around 850 of Hong Kong people of all ages, sexes, educational levels and so on.... a really nicely representative sample of people in HK.

He had an item as follows: 'postoperative transsexuals in Hong Kong should have the legal right to get married in their new sex'

48.3% agreed, some of them strongly.
19.6% disagreed, a few of them strongly.
(32.1% were undecided)

So those in support of 'W' 's case outnumbered those against by 5:2. That is very telling. It totally undermines any suggestion that HK is a conservative society that would not be able to handle something like this. Hong Kong people are ready for this. Judge Cheung apparently is not.

The judgement is in many ways worth reading. There are some interesting quotes. The judge is fairly clearly swayed by his own Christian beliefs about marriage p109 and elsewhere)
Also quite a lot of stuff about this unfortunate condition that transsexuals have. You may be reassured to know that he is at pains to stress how aware he is of the plight that transsexuals are in as a result of their condition. And throughout the entire piece his fear of same-sex marriage comes through (para 148, para 244 for example).