The story goes on a bit longer than I was expecting as I was playing through it, and it definitely gets more and more epic as you ramp towards its conclusion. It will let you know when you are starting the final mission too, to give you time to do other stuff if you want before wrapping it all up.
Also, if you are a fan of the comics I highly recommend playing through the flame side quests. Probably the thing that has me most excited for DLC or the next game.