I don't think I'm qualified to answer this because only hardcore masochists have sufficient experience in series that they hate. I think you'll need a lot of experience before judging a long running series as "the worst".
Some notable series that I did try playing a few games from and figured they weren't for me include Mario, Kirby, Sly, Ratchet, God of War, Sonic (ultimately), Call of Duty, Gears, Kingdom Hearts, Dynasty Warriors, most licensed titles, and sports games in general (liked some but eventually I got so bored and deleted the genre from my brain). But my limited experience doesn't qualify me to label any of them the worst. Among them I guess Dynasty Warriors is my least favorite gameplay wise, but if I paid attention to the story and played enough entries, my opinion would probaby change favorably.
