Secret babies are one of my favorite tropes, and I was almost giddy when Sierra first started coming out. Although Claude, the ML, found Sierra and their secret daughter way too early, I still enjoyed it and there was serious consideration of making this a special favorite... Then things started to somehow fall apart. First and foremost, the art was okay at the beginning, then started to wildly veer in quality, but overall it was underwhelming. Not terrible enough to warrant a termination of reading, but could have been much better.
What bugged me here is that you can sense that Sierra was made based on a much longer, more expansive novel with richer world-building and a complex societal structure. The manhwa bowdlerizes this to a lowest common denominator level, and meshes everything up in a carefree, almost painless slice of life. There are great moments that could have been used to make a highly charged, emotional story, but it mostly produces only lukewarm results.
Okay, Sierra as a FL was a bit of a Mary Sue (but not to a unforgivable degree), and her daughter, Blanche, was too unrealistically cute and prim and proper. Claude as a ML was more interesting, and it's so refreshing to see an emotionally needy, uncertain man who constantly craves, almost to a unhealthy degree, approval from Sierra. Most ML aren't like this, so in this regard it's highly unique. Although I found Claude too needy for my taste, it still represents a slightly more balances outlook on this emotional make-up. IMHO, the highlight of the manhwa was the crown princess, Elena. When you look at her from a more mature perspective, she's a deeply unhappy, emotionally wrecked young woman stuck in a highly desirable but disastrous marriage, constantly battling a invisible phantom her husband still revers and considers the perfect woman (that Elena is not). There is so much potential in this construction, but Elena is shown without much nuance, and thus remains a one note antagonist almost until the end when she's given some crumbs of depth but not quite enough.
Many other characters suffer a similar fate. Lady Lante, Lady Winston, Crown Prince... Are all glossed over for showing cute but repetitive and somehow unrealistic familial moments between Sierra, Claude and Blanche. I understand what they were aiming for, but at only 66 chapters, it was unnecessary to delve so profoundly into their daily life when there was a whole plot thread waiting to be dissected.
Crown prince, the main antagonist, is terribly underdeveloped, and his relationship with Sierra IMHO was shown in a completely wrong light. Precious dramatic tension could have been achieved but fails to ignite - Sierra hates him and feels so monotonically cold towards him, instead of showing her emotional doubts, her uncertainties over how she perceives him and how he perceives her. He was her fiancee after all, despite the political undercurrent of their liaison. And the reason for him being such an egg-head are never properly introduced.
Also, while Blanche is very cute, her character decracts from the story flow IMHO. This is a not a shojou, and we don't need overtly kawaii character cramping the style of what is otherwise quite a somber story. Plus her getting into the Academy and such storylines also didn't add anythings to the main plot. IMHO Blanche should have been a supporting char there to create some dramatic tension and serve as a backbone, but giving her the spotlight was a major oversight.
Okay, not to drag this down any more, ti still had plenty of interesting moments and I warmed up to Elena as a character, so overall it's not a total waste. Could have been much better, but even now, worth reading casually.