I really enjoyed The Snowmen too :) And I'm still not sure how I'd rank series 7 as a whole, but IMO the first half is among the strongest beginnings in DW, it's mostly the middle that lets it down. Maybe taking the filming gap in the middle was a mistake, they were going really big for the first five episodes, and they seemed to have lost momentum for those first few episodes after the Xmas special, the direction felt a bit flatter to me