I can't go on enough about how much I adored this drama. The premise, an autistic older brother being taken care of by his younger brother and their connection to a troubled author, had me curious.
Not only was the story beautiful, watching each character grow, mature, and *heal* but the actors were spectacular. I think that the drama would not have been nearly as fantastic without this cast - their dynamics and chemistry really perfected the scenes.
Seo Ye Ji was just as incredible as she has been in all the other dramas I've seen her in, but I was still very impressed by her wholehearted performance. Playing such an initially cold-hearted and stoic character is no easy feat that she pulled off perfectly.
Kim Soo Hyun made an exceptionally strong comeback with this drama being his first since coming back from the military. His acting brought tears to my eyes and induced goosebumps. He's also particularly beautiful, so win-win! :D
Oh Jung Se was also spectacular in his own right, though it was very odd to see him play such a unique character. Having 1st hand experience with autistic individuals, I can confidently say that he portrayed Moon Sang Tae masterfully. And he portrayed his growth in such a realistic and raw fashion - he too brought tears to my eyes numerous times.
Honestly, all the actors were absolute perfection, elevating this drama to the level of "masterpiece."

While the OST is really exquisite and the song placement is perfectly executed, the songs themselves are not my absolute, hands down, favorite ever. The songs are a bit eerie and sad, yet harmonious and calm (for the most part) - there's nothing objectively wrong with any of them, and the OST really is beautiful, but it's just not my 100% #1 favorite. Still exquisite though! ^-^

***SPOILER BELOW***
The only thing I do have a gripe about was how Ko Mun Young's mother survived that fall AND drowning to continue to terrorize Ko Mun Young 20 years later. I just have a really hard time buying this part of the plot. I think the writers were trying to mislead viewers to think the mother *couldn't* have survived for greater impact when we found out that indeed she did survive and she was right under their nose the whole time. But the medical and logical side of my brain is twitching at this plot device. :P
***END SPOILER****

Fortunately, the above-mentioned plot issue I have does not bring down the overall drama because everything else was so perfect. I will say though, be prepared for your mind to run wild with plot theories while watching the drama. There are so many clues, many of which are purposefully misleading where you'll drive yourself crazy trying to figure it all out. Now that all the episodes are released, do yourself a favor and go ahead and dedicate about 18.5 hours to binge watch the entire thing!

Overall, It's Okay to Not Be Okay is not your typical drama - it's super quirky and the character's and their lives are very unique to this story. But it has so many things that the average viewer can sympathize with and it just overall pulls at your heartstrings (and the chemistry is ON POINT) - not just the main characters, but the equally well-written side characters and their stories too. You can't help but be enthralled by their stories and it's quirkiness. The love story between Ko Mun Young and Moon Gang Tae that developed through their own healing was real and stunning. And watching Moon Sang Tae's metamorphosis, going from being child-like to a true older brother and adult (while keeping his character true to his autism) was magnificent. And witnessing them all become a healed family was extraordinary.

I have already watched this drama about 3 times (I rewatched each episode at least twice while it was airing because I just couldn't get enough) and I will most definitely be rewatching it again. If you're not sure about watching, give the first 2 episodes a try - I'm confident that that's all it'll take to suck you in. ^-^