It looks like they're going to kinda, sorta emulate Fox's 24 in that although there will be similarities between the first season and the second, there will be major differences as well. This, as opposed to one long multi-year story arc a la ABC's Lost.
The producers are approaching each season a volume in a book series. This way each season can stand alone and viewers don't have to watch an entire previous season to come up to speed for the current one. Show creator Tim Kring says that the 2 hour season finale will be:
"...intriguing more than frustrating... The idea was to end one idea of the show, one story, and then slingshot you into the next season."
The first season started out with the subtitle "Volume One: Genesis" while the second season will be called "Volume Two: Generations." Characters will be rotated in and out of the show, so I guess we shouldn't get too attached to any one particular character. We've already seen that in last week's episode where they killed of not one or two characters, but four!
I think this concept combined with the fact that they'll be producing a total of 30 episodes next season will go a long way towards combating the drop in viewers due to the serial nature of the show and will shorten mid-season hiatus.
These guys are on the right track for sure.
Source: Sci Fi Wire