I kinda hope Shredder's men turn on him *spoilors*
I had mixed feelings about the finale. In a way, it felt rushed. As awesome an idea as joining forces with the Shredder seemed, the potential for it seemed a bit squandered, and Shredder "killing" Splinter didn't seem well built up to (I think the main problem being WE JUST WENT THROUGH THIS STORYLINE).
I'm not entirely sure how they plan to resolve Earth's destruction. I'd prefer the black hole lead to an alternate dimension than fix it with time travel. If they fix it with time travel, then the rest of my post is definitely moot- but if they keep in continuity Shredder "killing" Splinter at the cost of everyone's lives, I'm hoping his henchmen defect. For the route they went, I think it's the most interesting consequence they could explore.
When Tiger Claw asked Shredder how he could do it and he's all like, "All that matters is my revenge," as they're getting sucked into oblivion, Tiger Claw had to be thinking, "Screw this, I'm starting a union!"