Firstly - I believe that where conventional chemical based agriculture is taking us with regards to wine and the truthfulness of possible expression of terroir is essentially untenable.
I think that biodynamic wine growers are at the forefront of morally acceptable viticulture and are (at the moment) making almost all the wines that I find myself truly excited about tasting.
However I have several reservations regarding the fundamentals of the biodynamic philosophy.
Whenever I listen to people talk about biodynamics there is usually a degree of romancing the past, harking back to a time when growers worked in harmony with the soil, when wines truly expressed their place etc. I very much doubt this was the case. Almost all the times I hear this kind of rose tinted reminiscence I'm extremely dubious.
The Steiner school of though grew out of the teachings of Rudolph Steiner who was a very interesting person, his views on teaching are very admirable, but there is a lot of spiritualism and romantic philosophy threaded into his work. Late on in his career he prepared a series of lectures on agriculture. Given that he was not a farmer I think that he was applying a series of beliefs and principles to another field. When you read through the list of preparations and treatments that biodynamics proscribes this becomes clear.
I have yet to see anyone really test the efficacy of any of the individual treatments, presumably this is because for biodynamics to work fully it needs to be adopted in a holistic fashion. I do understand this, however I can never quite escape the feeling that there is probably a core of really interesting and usable material at the heart of the teachings, but that it is too often dressed up in a lot of unnecessary and extraneous cladding.
That said, I do think that it is the best alternative currently available for conscientious viticulture. It respects the fact that viticulture, indeed agriculture exists within a very complex interlinked web of influences, and that many of these may be too small to identify but yet are still very important within the totality of the system. However I believe that the underlying philosophy is essentially a misunderstanding of these complex linkages, that has brought together a mish mash of spiritualism, astrology, a pagan reading of several different religions and a wishful reworking of the mediaeval doctrine that god shows us the essence of things through their shape and design.