I went to London several years ago and found it similar to Broadway. As others have mentioned, you have to pay for the program, which is fancier than a (free) Playbill. They call the Orchestra section the Stalls (which threw me one time when I asked an usher for the nearest washroom. She said, "Are you sitting in the stalls?" but her pronunciation was something of a cross between "stalls" and "stools" and for a second I didn't know what she was talking about. What did it matter where I was sitting, I thought--I was looking for the washroom. But I guess she wanted to send me to the washroom that was closest to where I was sitting). Their evening performances don't always start at 8:00 pm. They could be 7:30 or 7:45 or 7:15 or whatever. People seem anxious to be able to catch the train home, so the shows are more likely to start earlier. Also, the weekday matinee is not necessarily Wednesday. Some shows have a matinee on Thursday or Friday.
I was there 5 days, but managed to see 7 shows: The Man of Mode (at the National) with Tom Hardy, Hayley Atwell and Rory Kinnear; Daniel Radcliffe in Equus; Elena Roger in Evita; Avenue Q, Billy Elliot, The History Boys, and Cabaret (not the Sam Mendes production). I quite liked Evita, but the audience didn't seem that thrilled, whereas I found that production of Cabaret to be mediocre, yet the crowd was enthusiastic. The History Boys had been re-staged about 3 times in London; it's clearly a show that the Brits like, and the main show I had wanted to see (not having seen it on Broadway). Also, a song like "Merry Christmas, Maggie Thatcher" in Billy Elliot had much more resonance for a British audience than it would for a North American audience.
I don't think there's any difference in the quality of the productions or the acting. Broadway audiences might be more responsive (and fanboy/fangirl-ish), depending on the show. But having been to London only once, I can't speak with any authority.
Coach Bob knew it all along: you've got to get obsessed and stay obsessed. You have to keep passing the open windows. (John Irving, The Hotel New Hampshire)