If I can remember correctly (and with a bit of researching) the "great intelligence" has been in some of the old ones (like the second doctor) and was also in the Snowmen episode?
I think it's an old enemy coming back into the new series.
It was okay, it was a different twist of the sort, it honestly depends really. Of what you think.
From reviews there has been some good, some bad. I personally enjoyed it a lot
You'll have to enjoy it and find out really