Seeing Doomsday on this show is a bad sign in the first place.
So was having Lois on the show. I usually don't nitpick about things that are supposed to be cannon but, having Clark meet her, while still in Smallville, before he becomes Superman was something that always bothered me.
Well, I didn't mind it when it was a 4 episode guest shot. But when she became a regular and all she did was to be there for comic relief and add nothing to the show, that's when I started to get irritated with it.
And it is spelled "canon".