From my poin of view, the worst seasons are 3a, 4b, 6, and possibly 7. But I have to say even these seasons have some moments or plots that I really liked.

For 3a, I liked how they merged the piper and peter pan into one person and it fits perfectly with the arc. Especially enjoyed the episode where they reveal Peter Pan as Rumple's dad. It was an surprising yet reasonable twist, one of my favorite twists in the series. I also like the 3a ending where the curse wiped everything away except Emma and Henry where their memories were replaced with new ones.

For 4b, definitely the Cruella episode.

For 6, the most touching moment for me was when Snow and Charming "woke up" in the first curse and saw Emma. They chose to put others' happiness over theirs and closed the door to Emma. Then they drank the potion and went back to their cursed selves. I like how Snow gradually turn from sad to confused while holding Charming in the woods. The scene was just so emotional. I also liked the Dark fairy episode revealing her past. Fiona was just trying hard to protect Rumple. Her love to Rumple made her willing to turn dark and everything. I mean just look at what she did! She was born mortal but she studied hard to became a fairy! And she even created a powerful spell not long after she turned a fairy!

For 7, The scene I remembered till today was when adult Henry called teen Henry. A future self having a conversation with the old self. It was so emotional to watch. " What's next?" really hit me as I just finished high school as well when I first watched the episode. It always makes me think, would the future me be satisfied with my current decision? Would he be proud or regretted by me?