This is a gorgeous theatre. Like many London based theatres it's pretty old and the venue is all the better for it with its gorgeous chandeliers and intricately carved ceilings and walls.
There will always be a big production on at this venue as the stage is huge. You can usually get fairly cheap tickets if you're willing to sit up in the gods on the balcony but be warned that there are a lot of stairs to climb to get to that area. It's not for people that can't walk up many many stairs basically.