As far as franchises I really love:
-Final Fantasy: Played since the NES days, though I haven't been as interested since FF7... But those games, including the gameboy games, have been epic in my life.
-Halo - I love it. Other's don't. It's cool to agree to disagree. I feel like 343 can keep the game fun, and improve as they continue forward.
-Everquest. C'mon man! How did anyone not play this game? Heck, SoE is STILL MAKING EXPANSIONS! PEOPLE STILL PLAY! ZOMG! There are a number of better MMOs out there, but its hard to beat the bredth of the entire series. Kind of nuts.
see as far as all around quality goes I love halo, let's be honest has there been a bad halo game yet(not counting handheld), no there hasn't. But it's to this day still not my favorite multiplayer game of all time on the xbox, Mech Assault wins that title(this and Halo 2 are the only games I've played longer then a year exclusively) unfortunately they destroyed in it MA2 so bad it killed the franchise.
Halo also while being all around quality, has done nothing original and nothing game changing(PSC is right about this) that's why Mass Effect is also my favorite franchise between the two. And why Final Fantasy takes the cake, I think best franchise isn't just about what's popular COD has sold a bijilion copies but no one unless they're 12 would think it's an all time great franchise, it's about what has been a game changer, what was so far out and above the rest that it was a shock when released and FF has not done that just once but at least 3 times in its history.