That's not really fair, I think series should be 3 or more. Just because a series has 5 or more games doesn't mean a lot. CoD has a lot more than 5 games in it's series, but if we're all being really honest there's nothing massively different between the first and last CoD, apart from different stories and graphics. They never really do anything terribly innovative as far as I'm concerned.
Since I dislike the list, I'm saying Mass Effect. People can cry about the original ME3 ending all they want, but DLC's fixed it and I never played the game before the current DLC's were out, so I didn't have it ruined for me, I was smart about it!