I've been following up on this drama ever since Jingoo was cast for the role of Kim Woojin so I already knew how the story is gonna flow when I first watched it. I think the first episode is pretty good although the tone between Part 1 and Part 2 are so different. Not only in the timeline and environment but the way the plot went as well. Part 2 is much more lighter with a couple of comic relief scenes while Part 1 has taken a much darker route and the scenes were really intense especially between the twin brothers. 

I'm certainly intrigued and I hope the story will keep on getting better. 

I've only watched part 1 so far. It was okay, but it had alot less scifi than expected and alot more ordinary detective story vibes. I'm also upset that so far the only female character is an alien! Apparantly only males can be heroes, woman are all aliens tsk tsk! The writer must be a man who hates women. This is 2017, SOME DIVERSITY PLEASE! #UpsetFeminist #FemaleWhoLikesScifi
I liked it a lot. It's different to what I was expecting, but I'm satisfied so far.
I agree that the tone between the two part is so different! At first I was a bit lost but we quickly understand what's happening. I think I'm really gonna like this one, it seems so different to usual Korean drama.
@JulySnow2 I agree, there is certainly a lack of female characters in this story. While I wish there could be more women in the story, I don't think it's a bad thing that one of the female characters is an alien... We don't know much about the alien yet, her motives and her personality to judge that character as someone entirely displeasing. There are more female characters in Ep 2, and we do find out more about the lead female character, but yeah... I do wish they could've turned more characters into women. Anyway, this drama probably isn't for you, as it's been established that there are really more male characters and that the story is most likely gonna revolve around the twin brothers.

@Elisa Yup, and a lot of the questions from Ep 1 were made clearer through Ep 2. :D
I have to say that i prefer the 2007-part of the drama so far. 
Yup. And What I really like in this drama is that EVERY DETAIL is important. Remember when he talked with the professor about PTSD? Then.... We see what happens on smart Earth. I really can't wait to see what there is next
and the pilot episode was a suitable episode for this drama x) 
thanks should i watch this now or wait ?
@MrBanana Yes I prefer 2017 more too (you still do mean 2017, right? :D) Although thankfully, 2037 also manages to capture my attention well enough and I just love how it all connects back to the 2017 part.

@Elisa I do agree! I love how detail-oriented this drama is... and how great the connection is between the 2 eras and you realize it immediately as soon as you watch the other part. 

@soojungtash If you wait, then it could get pretty spoilery, if you don't then you wouldn't have to worry about cliffhangers. :D
@Aden Depends...I've seen the first episode, and so far it's really good. So if you like to binge watch dramas, wait. If you're like me and don't like binge watching dramas, watch it now. 

@MrBanana I also prefer 2017 more, ugh the brother story is so good! Both of them are great actors. But the 2037 part has me intrigued. Like which brother is main guy? How did the world get like that? What are the many awaiting secrets of SmartWorld? Who is the other twin brother? So emotionally, I like 2017 more, but intellectually I like 2037 more. 
How is Circle? I'm not interested in Sci-fi much but I like Yeo Jin Goo and I trust tvN. You can list the cons of this show for me. I'm all ears.
@Zig

CONS
  • The CG isn't perfect
  • BGM can get a bit too much especially in the first 2 episodes
  • You might get initally turned off by the different tones in the 2 parts (Part 1 is more serious Part 2 has a little bit more comedy)
  • Some people say they get confused about the story (although questions do eventually get answered every episode, so it's no biggie for me)

PROS
  • Amazing casting, everyone's doing an A+ job portraying their roles
  • The story - you'd be able to sense how it's been planned really well 
  • How the two timelines really connect so well to each other
  • Plot twist after plot twist after plot twist - this show is good at their reversals
  • No dragging parts