I second that opinion, but suggest that the museum's deserved popularity - especially with tourists - can often limit enjoyment of the environment, mostly because of queues and crowds.

For those who truly enjoy the BM, as a living, evolving resource and venue to be visited regularly, I'd suggest considering membership. It's £69 a year, and grants free access to otherwise paid exhibitions/events. It also grants attendance to members-only events outside usual museum hours. There's something really special about wandering the galleries during advent, with no crowds, and listening to live music (quartets, groups of singers etc) while drinking mulled wine and eating mince pies. Attending lectures, too, in which archaelologists and others discuss their digs and finds, is tremendously engaging. There's also a members' room in which to rest up.

For those with children, Young Friends membership for eight- to 15-year-olds is worth considering; I've paid for quite a few kids, and renewed year after year because they got so much out of the activities/experiences. The museum hosts Young Friends sleep-overs - some in the Egyptian section with the mummies.

Membership info: https://www.britishmuseum.org/membership

Young Friends: https://www.britishmuseum.org/membership/young-friends