Honestly, I'd have to say the Metal Gear Solid series. Now, before you start complaining and whining, honestly I played the games a lot, and every minute of playing the games was just a long, boring slog. The games are dark, they're monotone, they're overly gritty, they take themselves too seriously more often than not, and the humor when it DOES happen is just annoying, and often times insulting. The characters are bland, generic, and not a single one of them is a character I found to be all that likeable.
But I think what I hate most about the franchise are the people who throw a ****ing gasket any time I say how much I hate the franchise, not to mention all the people who feel the need to force me to go back and play the **** games over and over and over and over and over, yet the more I play them, the more I hate them. I really disliked the franchise at first, but the whiny, *****y fanboys who try to dictate people's opinion on the franchise made me loathe the series.