Tertullian was both a heretic and a schismatic, in that the group he joined that was in schism, the Montanists, were clearly heretical, and the heretical nature of their beliefs was documented by St. Epiphanios of Cyprus (who was also no fan of Origen; indeed St. Epiphanios along with St. Jerome were among the main opponents of Origen in the fourth century, with the Cappadocians on the other hand compiling the Philocalia, a selection of the useful and profitable writings of Origen).
The specific error that led Tertullian to embrace Montanism was his belief that those who sinned after baptism could not be forgiven, if memory serves.  But Montanism went beyond that, in that Montanus claimed to be the Paraclete (ironic that the man who coined the word Trinitas would join a sect the leader of which appropriated one of the primary titles of God the Holy Spirit).   This is of course a real tragedy.
Now, on the main thrust of this thread, the following is an intellectual analysis only, for I am not disagreeing with anything anyone has said on this issue - in particular, I am not disagreeing with the posts made by 
@ArmyMatt - although I do regard Tertullian as a heretic in addition to a schismatic, based on the writings of St. Epiphanios of Salamis in the Panarion, but I don’t know that ArmyMatt would disagree with that asessment, and also being a schismatic is a major problem and if I recall, one early church father, I think it was St. Clement, declared schism to be worse than heresy, although on the other hand we have to be careful to not use such an argument as a justification for an Pietist toleration of theological error; Pietism and its Anglican cousin, Latitduinarianism, and the Broad Church movement within Anglicanism and the Episcopal Church, USA, and the other mainline Protestant churches, caused so much damage, and ultimately led to these churches being taken over by heretical elements and in some cases going from broad churches that tolerated heterodoxy to narrow churches that do not tolerate anything resembling traditional Christianity - many clergy with the UMC, ELCA, UCC, and ECUSA have made statements that are … extremely doctrinally questionable, to put it mildly.  Indeed, herchurch, officially Ebeneezer Lutheran Church in San Francisco, is beyond heretical - its difficult to see how selling a “mother goddess rosary” and worshiping a mother goddess and a feminized trinity is anything other than the practice of a different religion (indeed, Metropolitan Kallistos Ware made the point in 
The Orthodox Way that the idea of worshipping a Mother and Daughter instead of a Father and Son would be entirely incompatible with the Orthodox faith).  
 Tertullian and Origen were respected members of the fourth century church, but Tertullian left and joined a heretical schismatic sect, whereas Origen on the other hand died in the peace of the church, and was greatly respected and admired by many, and indeed still is.   Now Metropolitan Kallistos Ware claimed Origen was anathematized for his belief in Apokatastasis but that St. Gregory of Nyssa wasn’t, perhaps because St. Gregory was St. Basil’s younger brother; if this is true, it would be most unfortunate, but the real problem with Origen is in some of his other writings, since we have also found works of St. Isaac the Syrian, who, like other members of the Church of the East at the time, adopted a view that Hell was temporary (see also The Book of the Bee by Mar Solomon of Basra).
The real problematic teachings of Origen rather are the speculations he engaged in, such as his speculation about reincarnation or metempsychosis, which was criticized by St. Epiphanios.
However, many Orthodox Christians are uncomfortable with the anathemas against Origen and Theodore of Mopsuestia, since Origen died in the peace of the church, and anathematizing him, and Theodore of Mopsuestia, who was the best friend of St. John Chrysostom, on the belief that would facilitate reunion with the Oriental Orthodox (which perhaps it would have had it not been for the subsequent violent persecution of them supposedly initiated by Justinian, the same man who wrote the Three Chapters which were then certified by the Second Council of Constantinople), because there existed a school of thought that Nestorius was enabled in his heresy by some of the more unusual ideas of Theodore of Mopsuestia - the difference of course being that Theodore of Mopsuestia did not use violence to persecute people who used the term Theotokos, but apparently he did object to the term, whereas St. John Chrysostom supported it.   However, both men died in the peace of the church, whereas Nestorius was an heresiarch, and Tertullian was a member of a heretical schismatic sect.
Thus, like with Roman Catholics, there are Orthodox Christians who are uncomfortable with the anathema against Origen, or some aspects of the Three Chapters, while agreeing with the theological work of the Fifth Ecumenical Synod, namely its rejection of all forms of Monergism (such as Universalism, Pelagianism  and, by extension, contemporary Calvinism).    There were also other heretics such as Diodore of Tarsus, and those who arguably delayed the removal of Nestorius, such as John of Antioch, who were not anathematized, and many other important church fathers who made errors, such as those in the first century who supported Chiliasm, which was officially rejected by the Second Ecumenical Synod in Constantinople, who we still venerate, such as St. Justin Martyr and St. Irenaeus, because individually, church fathers are not infallible.   So there are Orthodox who are uncomfortable with the idea of a post-mortem anathema.   
Conversely, in the case of Origen, I wouldn’t say he should be venerated either, and we can definitely say the Origenist sect as documented by St. Epiphanios in the fourth century was causing severe problems, and indeed, in the case of the Roman Catholic Church, it is because of his apparent support of the Origenists that Lucifer of Cagliari is only locally venerated by the Sardinians, but has never been regarded (to my knowledge) as a saint elsewhere in the church (and nowadays that would be rather awkward since many people believe Lucifer is the proper name of the devil, when it is rather a Latinized Hellenic translation of the phrase “Day star” in the Old Testament used to refer to the Morning Star in the context of Nebuchadnezzar, and typologically, the devil as well, because both are fallen, but there was a second century martyr named Lucifer who is properly regarded as a glorified saint, and who happened to have what would prove to be a very unfortunate name.  These associations are very powerful and it creates a bit of a conundrum with regards to how to ensure that the martyr by that name, and certain other early Christians who had that name, are properly  venerated, before that name became associated with the devil, without appearing to in any respect venerate the devil regardless of what name is in use, because obviously we don’t want to do that.    
Additionally, the Universalists in the Orthodox Church who are openly defying the Fifth Ecumenical Council, such as Dr. David Bentley Hart, should be rebuked on the basis of that council’s decisions, and in a sense, even though it might be uncomfortable, the anathema against Origen is at the very least theologically edifying, since Origen was a major proponent of full monergist Universalist apokatastasis (which was also according to some believed in by Diodore of Tarsus).
This last bit, the association between proto-Nestorians and Monergism, and indeed post-Nestorian members of the Church of the East and Apokatastasis, I would argue should not come as a surprise, in that Monergism seems to be a requirement of true Nestorianism, in that the Nestorians, in saying that Christ consists of two persons united by a single will, are engaged in a Monothelite and Monergist system wherein it is this single divine will that provides Christological unity, which is obviously so problematic as to compromise the doctrine of the Incarnation completely.   
If we embrace the Christology of St. Cyril of Alexandria and of the hymn Ho Monogenes, which was reflected also at the Council of Chalcedon, this undermines both monergism and monothelitism, since obviously if Christ our True God is fully God and fully man without change, confusion, separation or division, then with regards to His will he must be fully divine and fully human, and Monothelitism introduces confusion, and indeed it was disagreement over this issue that caused the schism between the Syriac Orthodox and the Maronites, who it is widely believed embraced Monothelitism, and also between the Copts and those Egyptians who embraced Monothelitism before it was properly rejected by the Sixth Ecumenical Council, which also anathematized Pope Honorius I under a post-mortem condition similar to the anathema of Origen and Theodore of Mopsuestia.   
Thus, I would expect more Roman Catholics might be uncomfortable with these post-mortem anathemas than Orthodox, because of the idea of a Pope being anathematized contradicting the extreme Ultra-montanism that we have.
Thus - with regards to Origen, I would say only those writings of his contained in the Philocalia with a C, compiled by the Cappadocians, not to be confused with the later Philokalia, a compilation of texts on monasticism, mystical theology and hesychasm by the 18th century church fathers St. Nicodemus the Hagiorite and St. Macarius of Corinth, should be used, or the Hexapla, if we are ever lucky enough to find an intact copy of it - the Hexapla being the first known parallel Bible and one of the books of antiquity the loss of which seems most unfortunate in terms of outlining textual variants with the Old Testament.    But we should remind people why he was anathematized, and more importantly, whether they agree with that anathema or not, why they should not embrace Universalism, because it is a form of monergism, and the Fifth Ecumenical Synod in Constantinople plainly declared Monergism was an error, and the fact that some saints we venerate such as St. Gregory of Nyssa and St. Isaac the Syrian subscribed to the idea of Monergism does not make it theologically correct.
Lastly, please pray for me as I have been recovering from severe food poisoning, and I am praying for all of you, my brethren.