Well, it’s because Season 5 was pretty much repeating the same formula from all the previous seasons. . .which isn’t a bad thing, but the formula was starting to become trite and repetitive. The doomsday mechanic is getting a bit played out.
Season 5 also had moments of extreme and utter stupidity, ranging from Jack’s Hoodie of Invisibility to his magical Jack Sack Power Pack which appeared to be even more potent than any cartoon character’s bag of tricks. Honestly, Season 5 really pushed the limits of believability, which just dragged the show down.
And Season 6 was. . .well, we all know how that turned out. Except for that 10 minute sequence where Bauer rode under a truck and took out Fayed with a Rolento-style super, everything else was just garbage.
[spoiler=Honestly, who doesn’t know at this point?]C’mon dude. It was obvious the second it was announced Tony would be returning. I’m sure he’s going to be all mad at everybody because Michelle died and he lost everything, and almost his life.[/details]
EDIT
I was just on the official site looking at profiles. Sweet Jesus Christ Nadia is so unbelieveably hot. Why oh why couldn’t you have been in a better season? And more naked?