This work was published in 1924. The reading of this work is as a follow on to Giles' works about religion in China, in which he skipped Buddhism for the reason that too much had been written on the subject. The work was intended for Christian missionaries. I have been following this up with a reading of the Buddha and Buddhism articles in the 1910 Encyclopedia Brittanica, with my usual suspicion of later scholarship.
My personal interaction with Buddhism is through the Chinese community, which generally leaves me with an impression of some sort of superstition based, prosperity gospel. Prayer is for health, wealth and successful children. The Western fascination with Buddhism centers on Japanese Zen, which Giles pointed out was a Japanese refinement to early Chinese Taoist philosophy, and really has nothing at all to do with Buddhism. So what precisely is Buddhism? I will give a few tentative thoughts, while retaining the right to revise them. The following are what I see as the original Buddhist notions and how they compare with Christian views.
1. Buddha's teachings were the product of self-revelation in reaction to other views of his time. In other words, he made it all up, although to the believers, his making it up was a true revelation. Of course Atheists will assert that all religious views are just made up, so that is really not saying much from their perspective. Of course, Atheists arrived at this conclusion through self-revelation. Christianity has a strong emphasis on the "Word of God", which is the source of truth, whereas the self-revelator is called the "false prophet".
2. Buddha's teachings were not referenced to God, yet deal with the souls of men and the supernatural. Whereas Christianity has a view of God as being outside of creation and having a purpose to all that is being done. Causality is part of the overall scheme of things, but the overall is done according to God's purposes. Buddhism has causality, but doesn't seem to have any purpose.
3. Buddhism has no concept of salvation. In Christianity, a sin is a permanent, fatal error, which is why our conscience retains this. The dealing with sin has to be done at a legal level that Buddhism doesn't have a concept of, thus, salvation is meaningless to Buddhists. From a Christian perspective, even if Buddha achieved perfection, he still lived a life of indulgence before perfection was acquired, and he is legally responsible to God. So far I don't see that Buddha had any answer to the guilt that comes with sin. In this sense Buddhism is similar to Modernanity, which has some sort of moral teaching but denies the reality of sin and the need for salvation.
There does seem to be some sort of a moral component to Buddha's teachings, although I would characterize them more as vague principles than anything concrete. The original Buddhist teachings developed into something quite different in China as various other notions were grafted onto the original. There were also distinct forms that developed outside of China, so the question, "What is Buddhism?" is not one that admits to a simple answer.