Just finished... okay, wow. Again, HOLY CRAP!!! I can't believe that was a live broadcast. If I didn't know that ahead of time, I would have thought this was filmed in advance and expertly edited. The camerawork, editing, and pacing were completely flawless. It's obvious ITV lavished all the expertise and experience they have from years of filming period dramas on the actual physical production here. The sets, as Scripps2 said, are so detailed and elaborate -- both the indoor and outdoor scenes were just looked amazingly true to life. I read that they used actual period furniture and they seem to have invested as much research into the costumes as they do for something like Downton Abbey.
All that said, I feel like I didn't get the emotional impact I usually do with The Sound of Music. I don't know what ITV's plans are with respect to releasing this in the U.S., but I suspect that when Americans see this version, they'll find it somewhat dour. ITV were obviously going for a much more naturalistic, verismo approach here, with incorporation of newsreel footage of the rise of the Third Reich (which got a bit heavy-handed toward the end) and acting and even singing that was much more restrained and understated. Emotional scenes were dispatched with a very matter-of-fact attitude. I don't agree that any of the actors were necessarily miscast, but some were definitely cast against the archetype that most of us are familiar with.
Chief case in point is Kara Tointon as Maria. Her Maria... was an odd creature. I don't know what to think of her, and I don't know how others will respond to her. "Earthy" is the first word that comes to mind. Her aura has a very salt-of-the-earth quality to it which I felt worked for Maria's penchant for disappearing into the Alps on her own. But I felt she lacked some requisite sweetness and innocence. She had warmth, especially with the children, but not the emotional fragility needed for the part, IMO. I felt emotionally disconnected from her narrative arc. Maria is written as naive, and Tointon seemed too world-wise. The direction played to that, though.
I thought the rest of the cast was excellent. Julian Ovendon had the most heart out of anyone on screen, IMO. His emotional arc worked for me more so than Kara's. I hate "Something Good", but I loved his rendition of it. There was ardor and pathos there. Maria Friedman's Mother Abbess was... very restrained. There was nothing particularly wrong with her performance. In fact, there was probably a lot to be commended about it. Her acting was excellent, especially in the scene leading up to "Climb Every Mountain." But the almost "inside voice", speak-singing approach she was directed to take for that number robbed it of its transcendent beauty. And, I admit, Audra McDonald spoiled me. 
The children were just about serviceable. Their acting wasn't as good as the NBC cast, but one thing I noticed: they all actually look like siblings. They had similar features looked like they could actually be related. Katherine Kelly was good as Elsa, but I admit I preferred Laura Benanti. She just had a certain spark to her performance, and basically stole the show from Carrie Underwood. On the other hand, I much preferred Alexander Armstrong to Christian Borle's OTT performance as Max. He gave an excellent interpretation of that role.
Over all, I am truly impressed with the quality of this production. The physical production and camerawork all blow NBC's efforts out of the water, and I am curious to see (if this ever gets shown here in the US or gets a DVD/BluRay release here) if this will force NBC/FOX/ABC et al. to up the ante on their production values, because... wow. This was just gorgeous to look at.