This "150th Anniversary Edition" seems to be simply a reprint of the 100th Anniversary Edition. In particular, the forward by Julian Huxley was written in 1958 and while it is still mostly relevant, it has dated badly in a few places.



The main text is Darwin's 6th Edition.



Darwin considerably amended Origin of Species through the course of its six editions. For example he first used the expression "survival of the fittest" (coined by Herbert Spencer) in the 5th edition and he first used the term "evolution" in the 6th edition. However, he also diluted some of his arguments in an attempt to deflect criticism. Most notably he made more allowance for now discredited Lamarckian ideas of hereditable affects of use and disuse, versus pure natural selection.



It is an open argument whether the 1st edition or the 6th edition best represents his real thinking. My 2 cents would be that the differences are relatively minor in the context of the overall work. The key driving ideas are well expressed in both and either is a fine start. Just be aware that other readers of Origin of Species may have seen a slightly different text!