OK, just saw the final episode last night. As a series, it never really got above a solid 5/10. Maybe a few moments of 6.
I think the series never recovered from the weight of trying to explain why MS was still alive. It buried itself under the most convoluted scenario and it took six episodes to escape it.
As stupid as it would have been, they'd have been better off giving us a cheap, easy explanation in the first episode, then cracking on with the interesting stuff, which is Schofield outsmarting people.
The only actual prison break that took place was a huge disappointment - they got out by default, not by design or ingenuity.