You know the more I think about this question the more I have a difficult time trying to think of a series where I've played a bulk of the games in said series. There are a lot of games I love that are part of a series but I never played and/or got into any of the other games in the series.

SimCity, as I mentioned earlier, is probably the best bet for me as I've played every major game in the series as well as a good number of the spinoffs.

Final Fantasy - yeah, I've played several of these, so I guess we can toss that up there as well.

Metal Gear Solid, maybe? Even though I quit paying attention to that series after MGS 3.

Pokemon I quit paying attention to after Generation 3 because that's when I ran out of money. xD

StarCraft doesn't really count because they've only got the two games.

Mario? Really only the early stuff (N64 and before).

Tricky question.