This drama is such a disappointment because the quality is below expectation. Usually, viewers are able to overlook imperfection regarding CGI, editing, dubbing, and other technical aspects if the story has quality. But, the story is this drama greatest weakness.

Setting/ Worldbuilding
Xianxia typically revolves the story around three realms: the Heaven of immortals and deities, the Earth of the mortals/ human-being, and the Underworld of the demons, spirits, and devils. Each realm has its own creatures, rules, limitations, and boundaries.

The immortals and deities can live for thousands years, They are born asexually from the ascension of lower beings as the results of their good deeds in previous life. They have superhuman ability and not usually died so easy (the only method is through the destruction of their primordial spirit so they cannot reincarnate). They live in the vast and unlimited heaven so usually, they are flying and teleporting. Immortals cannot intervene with lower realm affairs or use their ability in mortal realm. They can go to mortal world for tribulation or penance, and during this trip, they will forget their past.

Human being, animal, and plant are earthly creatures, have short life-span. They are relatively weaker, but can learn cultivation and martial arts. They live with family, in a sect, or a city. They have political entity to govern their affairs. They are crawling in the Earth on foot, horse, or carriage. Their culture and ways of living are richer. Their lives are bound to reincarnation circle. If they are good, they can ascend to godhood. If they are evil, they descend to be lower being.

Meanwhile, the demons, spirits, and devils are usually bad and on the lowest hierarchy of beings. After cultivating for years, they can have human form. They usually live as a nuisance to human, sometimes they eat human to get stronger. That is why they are hunted and killed. However, some of them are kind and not disturb human. They live in clan, so we have bird demon clan, fox spirit clan, etc. in the forest, river, lake, or sea.

Basic rules above are among common characteristics of xianxia worldbuilding. But, this drama breaks some important "rule". For example: Immortals are still immortals even when they go to mortal worlds (2 ML, 2 FL). They are very intervening, and without consequences. Human-being can have superhuman ability that makes them immune to injury and death even after severely wounded (ML). The spirit is not different to immortals as they can go anywhere i.e. the heaven without limitation (FL, the little flower spirit). What is more, the immortals act like human. They bleed when injured, they walk and run to reach certain place, and they are weak in fighting. They love and are jealous to each other. They are full of revenge and ill intention. Their living places are just like human palaces. Nothing wonderful and otherworldly. And, they can live, die, and revive as their wishes, not following the cycle of samsara/ reincarnation (just use a certain artifact to live again). Therefore, the time sequence of the story is messy. Everything seems happen in the present time. The past, present, and future are blurry. No good working timeframe.

I think, this mess is the risk for a too grand story (involving three realms), but no attention to details of each realm. This drama is weaker in the worldbuilding in comparison to xianxia like Love and Redemption (2020) which focus most of its story on the mortal realm. When they abuse the rules of the realms, the conflicts is resolved in lame manner. This drama uses deus ex machina, like when ML suddenly kills himself with unknown swords to stop himself going berserk, or when FL's heart weirdly has so much magical power, or when ML suddenly have magical pool to cure him, or when ML revives the Heavenly Emperor. There is not internal mechanism to solve their problems, like the use brain, analytical thinking, strategic talks, hard works, logical sacrifices, and risk taking for benefit. All depends on external power, weapon and artifact.

Story/ Plot
Immortal Samsara doesn't follow its premise. From the title, viewers may keep asking, what is samsara here? I don't know its meaning until the last episodes when ML confronts his father and learns about his parents story. His father is the demon king who loves and marries a goddess (his enemy), but ends up killing her in the end. So, he turns the time back from the beginning again for a different story and ending. Alas, the ending is repeatedly still the same, because his ambition never change and he never regret doing sins. It is the "immortal samsara". This is the more suitable back story (and the birth of an exquisite god as the result of their love), IMO, rather than the story of twin lotuses which has no significance for the realm, making this like the story of the prince and pauper. The story should use the ML's point of view.

Storywise, this drama lacks good story structuring. It can be more interesting and suspenseful, if the story progresses back and forth to reveal the mystery of the past and hidden identity of ML, and the reason behind why love is forbidden in Heavenly Realm sooner. Alas, this drama put too much emphasize on the ill fated relationship and the romance between ML and FL which is not important to the overall story and conflict. It will be a better story if in the end he becomes the Heavenly Emperor and takes the FL (a mere spirit) as his queen to reward her love, loyalty, and sacrifice, as the result of him learning about his parents, his identity, his enemy, the long conflict between immortals and demon, and the mistakes of the strict rule. This drama wastes an interesting plot where the enemy successfully kills the former Heavenly Emperor and impersonate him. It is never seen in previous xianxia. This drama could have interesting revenge and justice story rather than a mere romance and stupid double suicide in the end.

Characterization
Cheng Yi and Yang Zi are very good actor and actress. But, their potential are wasted because of the problematic story. ML and FL are very two dimensional. Their personalities are predictable, their behaviors are predictable. The writer should dig more on the psychology of a lowly ang young little fairy in the front of the greatest deity. They fall in love too easily, which is illogical considering their statuses. FL should be more selfish (think more about her self) because she is still too young, weak, and needs protection, and wishing for a future and pride. She shouldn't prefer death than life so easily and work harder to maintain her position in the heaven. But, they write her to be a lazy woman and have no aspiration better than a play writer. They can create her to be more interesting with describing what kind of story she would like to write and it will show us her life values, idealism, and personal difficulties as a person, and how it connects to the ML's aspirations and values. The way they introduce ML to FL is so not romantic (as a turtle flipper), downgrade him to a level of child, while he should maintain his dignity as a responsible and wise thousand years old deity. How could he fall in love so easily to a "baby"?

Other supporting characters are generally useless, like a decoration in the background when they are just standing and watching. Supporting deities do more talking than doing something to help, going here and there in a crowd, screaming, and being angry/ sad. They act like ministers in the mortal court rather than deity with specific duty and certain ability. They solve problem through debating, rather than doing something magical. The demons in the valley are also just cute, but useless. The heavenly soldiers are so small in number, like 20s. They should use CGI to multiply them and create a majestic war battalion with good fighting skills to counter demons.

Music
Nothing memorable. No banger. No heart punching beats. Too flat. Too cheesy.

I hope future xianxia learns something from this failure.