It was a little strange at first, since you were seeing the action at a remove, and perhaps it seemed a little flat. The opening scene had the sound of a heartbeat, and in the theatre you would have felt that vibrating through you. But I, and the rest of the audience, soon became engrossed in the story.
The two main leads were Benedict Cumberbatch and Jonny Lee Miller, who have been alternating the parts of monster and scientist - the version I saw had Benedict as the scientist. The play opens with the monster coming to life, so you start with sympathy for him, although he does monstrous things later on. He was dumb to start with but learned to speak, and ended up quoting Paradise Lost. It's been ages since I read the book, but I downloaded it and this was how the monster was portrayed in the original - it's the subsequent films that made him speechless. The scenery wasn't elaborate, but it quickly sketched in what the location was supposed to be. And there was great use made of a hanging path of lights, stretching from the auditorium onto the stage, although that was one of the things that might have been even better if you were in the theatre.
There were advantages to the broadcast though, since the play wasn't just shot from the front with one camera, but from many angles, so you could even have close-ups, and views looking down on the stage. These were used very effectively in the story, and I wonder if that was through having a film director choosing the shots. There were some gasp-making surprises in the play, and one moment of true horror where he tells Frankenstein's wife "I have learnt how to lie."
Definitely worth the money, and I'd consider going to see another "live" performance of a play. They also do operas and ballets, and I might try one of the latter since I used to go to a lot of ballets when I lived in London.