I'm a lead farmer, mother lover!
As the title has indicated, below this there will be quite a few spoilers for the book Halo: Cryptum. If you do not wish to find out beforehand, please leave. They gone yet? Good. For those still with us, Halo: Crpytum has a lot of underlying themes and allegory I think that would be nice to look at.
Theme 1: "Those who cannot remember the past are condemned to repeat it." - "Reason in Common Sense", volume 1 of "The Life of Reason"
A simple theme that we see throughout Crpytum. This quote is misinterpreted by many as "History repeats itself." We learned of the Human-San'Shyuum battle against the Flood. We also learned that the humans were able to win, discovering a cure of sorts and fight them back. Interestingly enough, due to the forgotten lesson included, not only are the Forerunner forced to fight the Flood (and lose), Humans once again must battle the flood in the distant future with the assistance of a different pact (Sangheili/post-Schism covenant factions).
Theme 2: Religious Allegory
So to say that Halo has a lot of religious allegory is really understating things. From the fact that the main nemesis is called the Covenant, to the Ark, to the fact that the Gospel John 1:17 speaks of the great flood - Cryptum continues Halo tradition with gusto. Where is the Christian Allegory here? Simple. The Didact has extremely large connotations to Jesus himself. A man that was respected and esteemed by all, trying to uphold the mantle of life (albeit in different ways), betrayed by others who disagreed with him on council. His exile reminiscent of Christ's death only to be raised at a later time. His spirit going so far as to merge and transfer within Bornstellar. Now my reading of this was a bit muddled, and it could be argued that there is more Buddhist allegory here. Meditation to attempt and find nirvana/peace. Reincarnation in different forms and better lives, which is clearly seen if you compare the Didact (A Warrior-Servant), who later is technically genetically imprinted onto Bornstellar (A Manipular who after first mutation is primarily a Builder but also imprinted with Lifeworker and Warrior-Servant details), whom by the caste system is of higher standing. There is even Shinto allegory as the Domain is more or less a collective consciousness of Forerunner ancestors, worshipped by the living and prayed to for answers.
I'm sure there's even more I may not be touching upon with religious examination so feel free to let me know and I'll include it in this post. If there's other themes too, think on it and let me know. Now onto what is solidified and learned:
Humans
This was the biggest surprise for me. A human intergalactic empire having once existed and then even going so far as to war with the Forerunner? They were then subdued, quarantined to their planet Erde-Tyrene (Which btw, in German Erde means Earth for those who don't know), and then systematically devolved into several subspecies. I'm curious as to how the other side-subspecies will come into play and we see what happens to them. Clearly Chakas is a early human example however what comes of the Florians (Riser's people).
Forerunner
Possible brethren to Humans and a lot more hot-headed then we originally thought. They displayed a wide variety of emotions which we don't often attribute to "higher beings." Betrayal, Rage, passion, compassion.
Precursor & "The Prisoner"
If the prisoner is indeed a precursor and not a gravemind as implied we know them as physically large creatures that resemble monstrous Humans with forked tails, 4 massive upper arms and powerful bodies. They also can live millions of years in age. Apparently he blames Forerunner for the fall of the Precursor though if they are directly to blame is unknown. Here's a key detail people seem to be forgetting: He was imprisoned. He was imprisoned by the Precursor themselves as shown by the locks. It is entirely probable that he was a criminal even within precursor society, exiled to a remote planet and locked up to prevent him from doing future harm (which would make sense if the Precursor truly believed in the mantle, they wouldn't have him killed). It is suggested by some in threads that the Precursor as retribution against the Forerunner created the Flood, however this is refuted still.
San'Shyuum
They changed dramatically in the thousands of years. In the beginning they were a race embroiled with a "sensual" beauty. A term I don't think any of us would use to describe the Prophets we know and hate from Halo 2/3. They formed an alliance with Humanity to combat a common threat in the Flood, and hope to expand afterwards, combating the Forerunner. However they clearly didn't command much pride, as as soon as the battle turned against them, they surrendered. In the years following their forced quarantine we see their entire society changed to something we recognize more. Then they are all killed by a Halo activation by the Forerunner, putting them down for their rebellion.
Flood
Started as Spores and grew from there...Wooooot?
Other
The only other races really touched upon were the Huragok (Engineers) whom are pretty much exactly as we know them. Efficient, only interested in work, and proud of their flotation ability in different environments.
Ok, I'm good now. Thanks for any reads/comments all.