From someone who has not watched the OG (excuse me this is my first review!):

I found this drama to be quite enjoyable. It is definitely not perfect, but still fantastic watch.
-Story
I personally have a fascination with dramas that explore time travel, so it was interesting to me right off the bat. Some people seem to find multiple and interconnecting timelines/characters confusing, I usually do not though so I was able to follow along well. There were one or two moments that through me off, but I was able figure it out pretty quickly. If you do struggle with keeping track of things though then you will find the drama confusing, luckily if you read in the comments there are some nice people who have outlined the timelines for you! I do think that everything made sense though (for the most part) and they were able to tie things up pretty nicely, unlike many other dramas out there. The first few eps were definitely the best, but the rest of the drama still held my interest. The mystery portion was done relatively well all though not as exciting as it could have been.

-Cast, chemistry, and romance
Some people in the comments and reviews seem to be questioning these to a great extent, but I disagree. I think the cast did a wonderful job and I was definitely able to feel that the fl was playing two different people. Her acting is a little off in moments but overall she still was successful in her portrayals. I also disagree that there wasn't chemistry between the leads or that the romance fell flat, I did not feel that at all. The building of the romance was pretty well done especially the portion when they were in college.

-Other
The cinematography was very picturesque, and the setting/sets were also well done, this drama is definitely very visually appealing. I personally liked the songs and OST and did not find fault in it, if you did not see the OG drama this will not bother you like it does some in the comments. Overall, I think you will enjoy this drama if you are able to keep up with everything and try to think from the characters POV in regard to their actions and motivations.

One also needs to understand that many here in the comments and reviews are not objective since they have seen the OG which they have a developed a strong attachment too so it is natural that they will be overly critical of the remake - which is of course going to differ from the OG. These people are looking to find fault with the remake from the get-go, so they are not going to look at this work with fresh and open eyes. Those who watched the OG are also not going to be as impacted by the revelations and plot developments since they already know what is to happen. If you are going into it without the OG as a refence you will most likely enjoy it as I have.