Where should I even start from?
The skilled action scenes that are just perfect enough to create tension without being too draggy, the natural comedy that is much needed after intense scenes, especially when it appears in least expected scenarios, the medical aspect that is flawlessly intertwined with the military portion of the drama, or should I start from the love story itself?

Many dramas have a mixture of genres, but fusing them together so beautifully is what matters, and this drama not only succeeded at it, but you may say it mastered it even!
There really were no dull moments across the whole drama, which is quite rare honestly. Usually, somewhere in the middle, dramas seem to lose their charm, making the audience wish to just finish it off as quickly as possible, just to get to the end, and this is definitely not the case here at all. In fact, not sure if it is a plot driven or character driven story but it seems to be a mixture of them both as well, so there's always something that is developing whether it is the story line or the characters themselves.

So let me summarise the things I appreciated and loved the most about the drama...

~STORY pace
Its relatively fast pace is very easy to follow without getting bored at any time, especially since there's always something happening, almost as if there's no time to breathe. Having said that, even withing its action pack plot involving natural disaster for instance, it has its own moments of peace and tranquil, where characters are seen, reflecting, regretting, laughing, crying, mourning...growing really, keeping it very balanced and realistic.
Talking about the love story in particular, I'm quite surprised how though their professions are the polar opposite, there's still some sort of commonality which acts as the base upon which their relationships develops. The secondary couple's love story is worth mentioning too, just like each and every other characters's story as well.
It is truly admirable how it manages to keep a high quality from the very first episode till the last one.

~CHARACTERS, every single one of them!
It is very rare to find a drama where every character is loved, and this is one of those dramas for sure. In fact every character in this drama seems to be a scene stealer, whether they appear for one or many scenes, it feels like they've always been part of the story! Be it the medical or military team, the way each one of them showed their courage, vulnerability, sincerity and humanity is really commendable!
Not only the chemistry between the leads is heart touching, heart flattering or even heart wrenching, the chemistry between every other characters in general is what keeps the drama tied up together till the very end. So every emotion comes across very sincere and heartfelt.
Special mention to the acting of the lead couple, the way their eyes conveyed so much throughout the drama, maybe even words couldn't do justice in those scenes, so very well done to both Song Joong Ki and Song Hye Kyo. Also the secondary couples' chemistry was top notch too, as most of the time they were parted, still their love and passion towards each other was very evident.

If you are wondering if it is a 'over-hyped' drama, then let me tell you that that's what I thought too, and then decided to give it a go after all these years. Eventually I was surprised myself realising how it didn't disappoint me at all! So I would of course recommend this drama if you want to experience an adventure of sincere love, team work at best and honest portrayal of vulnerable emotions.

PS. The cinematography is wonderful, whether it is how beautiful locations were shot or even how the disastrous settings were created and filmed very realistically! The OST also was very adequate, which helped enhance emotions and create unique atmosphere.