I personally started with season 2, because I saw a video that motivated me to watch it as soon as possible.
IT WAS THE BEST DECISION I MADE!
I highly recommend watching this series, because the storyline is unique and it is not your usual drama. It has a lot of romantic moments, funny scenes and interesting, plot twisting ones as well. I really enjoyed that this drama is not childish like other chinese dramas. It sometimes reminded me of American series, because they approached themes like serious relationships, pregnancy, intimacy, periods and family problems.
The chemistry between the main leads in my opinion is just amazing. You can see that they are really comfortable with each other. Something else, that i really enjoyed was that they did not only focus on the main leads, but took time to tell the other characters' stories as well.
Besides this, the sound track is really amazing.
If you like dramas that have an interesting storyline and that expand the romantic relationship well, without making it childish and aboard themes that you can relate to, than this is for you!