I've come across several critiques of Mahayana and specifically Zen (Chan), like the following:
1. It (Mahayana+Zen) postulates Buddha-nature which is contrary to anatta
2. It (Mahayana+Zen) asserts our original enlightenment which makes no sense - why practice then?
My answer to the above:
One should read and study carefully the Lankavatara, Prajna Paramita and the Mahayana Mahaparinirvana Sutras.
From the Lankavatara Sutra:
Then Mahamati said to the Blessed One:
In the Scriptures mention is made of the Womb of Tathagatahood and it is taught that that which is born of it is by nature bright and pure, originally unspotted and endowed with the thirty-two marks of excellence.
As it is described it is a precious gem but wrapped in a dirty garment soiled by greed, anger, folly and false-imagination.
We are taught that this Buddha-nature immanent in everyone is eternal, unchanging, auspicious.
It is not this which is born of the Womb of Tathagatahood the same as the soul-substance that is taught by the philosophers? The Divine Atman as taught by them is also claimed to be eternal, inscrutable, unchanging, imperishable. It there, or is there not a difference?
The Blessed One replied:
No, Mahamati, my Womb of Tathagatahood is not the same as the Divine Atman as taught by the philosophers. What I teach is Tathagatahod in the sense of Dharmakaya, Ultimate Oneness, Nirvana, emptiness, unbornness, unqualifiedness, devoid of will-effort.
The reason why I teach the doctrine of Tathagatahood is to cause the ignorant and simple-minded to lay aside their fears as they listen to the teaching of egolessness and come to understand the state of non-discrimination and imagelessness.
The religious teaching of the Tathagatas are just like a potter making various vessels by his own skill of hand with the aid of rob, water and thread, out of the one mass of clay, so the Tathagatas by their command of skillful means issuing from Noble Wisdom, by various terms, expressions, and symbols, preach the twofold egolessness in order to remove the last trace of discrimination that is preventing disciples from attaining a self-realisation of Noble Wisdom.
The doctrine of the Tathagata-womb is disclosed in order to awaken philosphers from their clinging to the notion of a Divine Atman as a transcendental personality, so that their minds that have become attached to the imaginary notion of a "soul" as being something self-existing, may be quickly awakened to a state of perfect enlightement.
All such notions as causation, succesion, atoms, primary elements, that make up personality, personal soul, Supreme Spirit, Sovereing God, Creator, are all figments of the imagination and manifestations of mind.
No, Mahamati, the Tathagata’s doctrine of the Womb of Tathagatahood is not the same as the philosopher’s Atman.
Countless Patriarchs of Zen/Ch'an have warned of false attachment and understanding of Emptiness:
...because most cultivators are still attached to "duality," and have not reconciled essence and marks, existence and non-existence, noumenon and phenomena. That is why they embrace essence to reject marks, noumenon to reject phenomena, Emptiness to reject Existence, and vice versa -- thus creating disputes, doubts and perplexity.
Little do they suspect that there is mutual identity between noumenon and phenomena -- phenomena are noumenon, noumenon is phenomena.
If we divide them and consider them separately, phenomena are not true phenomena, noumenon is not true noumenon.
This is true also of essence and marks, existence and non-existence and other dualistic dharmas.
For this reason, the Vimalakirti Sutra speaks of the non-dual method to destroy this attachment.
Non-dual means reconciling all things, penetrating into their very nature; it does not mean "one." This is the true realm of "Mind-Only."
Any other doctrine based on the Dharma Doors of Existence or Emptiness is merely an expedient for teaching purposes.
The Sutras state:
To tire of and abandon "conditioned" virtues is the action of demons.
Yet, to be greedy and attached to transcendental, unconditioned virtues is also demonic action.
Ancient sages have also said:
Conditioned dharmas, while illusory, cannot be abandoned if we are to attain the Way.
Although unconditioned dharmas are true, if we become attached to them, our wisdom-nature will not be comprehensive.
These words clearly show that on the path to Enlightenment, unconditioned and conditioned dharmas, noumenon and phenomena are inseparable.
It is also stated in the Treatise on the Middle Way:
Because common sentient beings grasp at external forms, the Sutras destroy this attachment with the truth of Emptiness.
If as soon as they are free of the disease of attachment to Existence they fall into the error of grasping at Emptiness,
there is no medicine that can help them.
Of the two types of attachments, to Existence and to Emptiness, the latter is the more dangerous.
Both the Lankavatara and the Esoteric Adornment Sutras warned:
It is better to be attached to Existence, though the attachment may be as great as Mount Sumeru, than to be attached to Emptiness, though the attachment may be as small mustard seed.
Attachment to Existence leads to mindfulness of cause and effect, wariness of transgressions and fear of breaking the precepts, as well as to such practices as Buddha and Sutra Recitation and performance of good deeds.
Although these actions are bound to forms and not liberated and empty, they are all conducive to merit, virtue and good roots.
On the other hand, if we are attached to Emptiness without having attained True Emptiness,
but refuse to follow forms and cultivate merit and virtue, we will certainly sink into the cycle of Birth and Death.
3. It (Zen) dismisses sutta study
4. It (Zen) is anti-conceptual and promotes no-thought
The Sixth Patriarch of Ch'an foresaw this kind of thinking:
http://www.dharmaweb.org/index.php/Sutr ... structions
"A bigoted believer in Nihilism blasphemes against the Sutras on the ground that literature (i.e., the Buddhist Scriptures) is unnecessary (for the study of Buddhism).
If that were so, then neither would it be right for us to speak, since speech forms the substance of literature.
He would also argue that in the direct method (literally, the straight Path) literature is discarded.
But does he appreciate that the two words 'is discarded' are also literature?
Upon hearing others speak of Sutras, such a man would criticize the speakers as 'addicted to scriptural authority'.
It is bad enough for him to confine this mistaken notion to himself, but in addition, he blasphemes against the Buddhist scriptures.
You men should know that it is a serious offence to speak ill of the Sutras, for the consequence is grave indeed!
"He who believes in the reality of outward objects tries to seek the form (from without) by practicing a certain system of doctrine.
He may furnish spacious lecture-halls for the discussion of Realism or Nihilism, but such a man will not for numerous Kalpas realize the Essence of Mind.
"We should tread the Path according to the teaching of the Law, and not keep our mind in a state of indolence, thereby creating obstacles to the understanding of the Norm.
To preach or to hear the Law without practicing it would give occasion for the arising of heretical views.
Hence, we should tread the Path according to the teaching of the Law, and in the dissemination of the Dharma we should not be influenced by the concept of the reality of objects.