Even though I watched the original a couple months earlier, I could still enjoy and cry with A Time Called You just like an individual project.
You have to watch with an open heart and try to avoid the comparisons because it will affect your experience. Besides, each actor put their own impressions and thoughts into their characters. I think the idea here was never fully copy the original, but bring the essence of it, and they did that well.

Yeon-been was excellent portraying the differences between Jun-hee and Min-ju, and Hyo-seop was able to convey Si-Heon's charisma and pain.
I don't get why people got so critical about how he portraid old Si-Heon, because I could understand that after all he had to go through, alone, he was just tired and stopped caring about his appereance, since he was so invested in fixing what happened.
And thats okay, I think both versions of the character, original and remake, are valid.

About the time lines, you need to be patient and pay close attention to details, because by the end it will make sense.

I think the one thing that bothered me a little was that they cutted out some of the relationship's delevopment between the characters. It was sentimental, but in a more straight way.

I really liked some changes the writer made like Yeon Jun's story (it was less darker than the OG and helped me to understand what actually happened with the character), and the OST also turned out to be one of my favorites. I wasn't expecting it. I've been listening the songs since the release. I just wished Netflix had released the acoustic version of NewJeans' Beautiful Restriction on streaming, because I LOVED it ever since I heard in the promotional trailers.

For those who have never seen the original, A Time Called You will be quite a journey and will hold you in your seat while the story unfolds.
I totally recommend you to give it a try and just enjoy the ride. I've watched three times already, so it's worth it