Quick answer here: Is it worth to watch? Maybe, but mostly no.

One of the biggest mistake in making a story is by not having the main characters the most interesting one consistently. The synopsis really do not hold much of what's in this, as the drama itself have it's several conflicts scattered all over the place. The direction of each really doesn't place cohesion to every set of events, therefore, the overall flow is substandard, not just for the story but for the characters as well. After some episodes you will develop incurious feelings towards the main couple and enjoy the second leads more (e.g. Sun-woo, Hye-sun and Jae-jin) that which really the reason why I lasted up to episode 14 before I dropped it completely despite of being bored since at the very middle of the drama.

One of the main reason I watched this is because the cast are pretty big, expecting this is a well made one. Sadly, even good actors and actresses cannot make a bad oriented drama good. There's no chemistry between the main couple and the traits of the main girl (Lee Dam) is inconsistent— which can be irritating to some viewers with her sudden childishness.

Also, Gye Sun-woo (Bae In-hyuk) deserves much better. He is obviously made just to suffer for the sake of the main couple (and yet he is much more interesting every time he comes to the screen than the actual main lead interaction). He got the actual change and development in him.

Note: I haven't seen the source webcomic (this is a drama review after all so this is drama-only thoughts), but I also read a lot of manhwas for years now and I have a feeling that the story is better laid in the comic and it wasn't just translated well into this drama. The kdrama True Beauty is actually kind of different to its source manhwa, that which makes it decent as a kdrama itself.

TL;DR: I do not really recommend this, but if this is mainly your type of genre, then maybe it can be worth it, especially just for the first half.