Truthly I would still keep watching these on dvds but these episodes I thought were crappy and the worst for each season:
S1: I was tied at the last moment between Shimmer and Reaper where one kid used meteor rocks to turn invisible and the other is a freak who can kill people. And the worst would have probably been Reaper. Reaper I just thought had a terrible story, a terrible villain, no other important plot points with any of the other characters, and I hate that he killed the puppy >:l The only thing i liked was that it showed that its not easy for villains to kill Clark Kent when he cant even be fully affected by death itself lol.
S2: the worst is Rosetta (KIDDING)! the real worst was another tie between Suspect and Visitor which both i tend to skip on the dvd's once in a while when I dont feel like watching them but the worst worst is probably Suspect. Sorry but the concept was good it just didnt entertain me in any way. It was kinda like one of those episodes where eh i'll watch it while doing homework or something. I liked Jonathon being framed, Lionel being shot, but I kinda wasnt fond of lex in any way this episode which is my main reason why I didnt like it. He just didnt seem like lex in this episode whether he was good or evil.
S3: the worst for me was Delete. I just didnt really like the story between chloe and this hacker chick. I did like killing Lana and the Kents but I thought being controlled by data stuff like they showed didnt make sense to me and I felt was stupid. I also had another problem with Lex in the episode because he was connecting to the villain which is smart for the writers but it totally ruined it for me when I started seeing him a little more psycho then normal (not like the kind in shattered lol) just pyscho like the girl.
S4: This is one of my favorite seasons so I didnt really have a worst episode (thank god lol) but I did dislike the ageless baby powers and stuff but clark and lana's parenting actually made it better. Surprisingly thats it for Season 4
S5: Surprisingly guys my worst wasnt thirst as most people think because I liked it truthfully lol. My worst was Tomb because I just hated the main story. The side stories with the main characters was fine but chloe being possessed by a random dead girl who gets a random lighting strike and wakes up to kill a random nurse? Sucks.... I like how they were trying to give Allison more acting breakthroughs and she did a good job just the writers and director failed.
S6: worst favorite and probably the same for most people was Noir. The black and white episode centered on a stupid random thief that we never actually meet that much, the plot of focusing on jimmy and changing his character was stupid. Lois being a hooker or whatever sucked, Lana being the villain in the past terrible, I just hated every one bit of that. I actually skip this episode every time I watch season 6 unless im doing something else at the same time.
S7: Worst was probably Action. I like Warrior Angel connections and stuff but this episode kept reminding me that Clark was sitting on his couch all season waiting for trouble to come just like Oliver said it in Siren. The story was ok, I actually liked all the characters except I hated clark sadly. That is the worst a writer and director can do is make us hate the main character more then the others. Caroline Dries wrote it and Mairzee directed it and Mairzeee did an good job but Caroline that was an epic fail of a episode for Clark.
S8: In season 8 my worst was actually Turbulence but for totally different reasons then the rest. It was just wierd and crazy. It was way to dark and wierd with Jimmy coming back, Tess and Clark in the plane was kinda like a ticking bomb ready to go off the whole time, Davis killing people to control the monster was wierd because by killing people he is the monster. Like i said wierd!!
S9: I liked it all also but if anything I would say I wasnt to fond of the episode Crossfire mainly with the Rick story and stuff involved with him. Was boring.
S10: Liked it all as well but had minor problems with episodes Isis, Harvest, and Booster. Not serious just minor.