People probably liked it because of Mew and Willy. It was really a showcase for Mew's talent. I liked it because it was so different from the typical lakorn. Both Sai and Chan were different from the usual n'ek and p'ek and their relationship was also unusual. They were complex grey characters instead of the usual cardboard goody 2 shoes.
Sai wasn't really likeable but you understood and pitied her. I know a lot of people didn't like the "unhappy" ending but I did. Everyone made a very real mistake and they all paid for it in some way. Sai lost her dad, her sister, and Buree and Chan. Buree who prioritized morality over love, lost Sai. Looksorn took a chance on love with a guy she knew didn't love her and was the biggest loser. Chan lost both Sai and Looksorn. That they were all able to learn a lesson and move on to become friends was a happy ending in its own way.
I never saw Sai as a n'rai in the old version. She wasn't even a rai n'ek. All her actions and feelings were very real and never over the top like a n'rai. That said Chompoo does come off like a n'rai in the teaser.