When something is this good it will of course simply come down to a bit of nit picking. I missed the Routemaster bus as I suspect did 99.99% of the audience but there were a couple of things I picked up on. Correct me someone please, if I'm wrong.
A common fault of British series that have an eye on American sales, and who can blame them for that, is the introduction of American words and phrases that might have passed into common use in 2013 but hadn't over 60 years ago when these stories are set. Compared to many this production is an Americanism free zone.
However, as far as I can remember, the table used by the night staff on a Nightingale style hospital ward of the time would not have a plaque on it saying 'Nurses Station' and British military establishments did not have any areas described as 'Off Limits'.
Just little things but they show how closely we're watching and I for one can't wait for the next episode.
As for the excessive number of commercial breaks, you can reduce any 2 hour programme on ITV to about 95 minutes by recording it on your PVR, for instance a Sky + box, and fast forwarding through the breaks. Keeps you sane and gives you back 25 minutes to do something else with. Simples. (Oops, its those adverts again)