The next one absolutely has to be the last season. They've kinda butchered the show. I still love it, but it's unrecognizable now from the show that hooked me.
It's a totally different show now, that's for sure, but towards the latter half of this season, it at least began to feel a bit more like Fringe of old. But I DO miss the original versions of the characters (though Peter has remained the constant in this show - he's like the Desmond of Fringe!)
Although I'm not expecting it with only 13 eps next year, I wish they would touch upon what happened to Sam Weiss and where he went, and more about how the damn machine was built in the first place.