It's spectacular.
Quite a small auditorium, which has been specifically built for it, so you would get a good view from anywhere I think.
There are standing/dancing tickets available at the front but the seating areas are well tiered so they don't affect your view.
Yes people sing along, but what isn't allowed is mobile phone use so no annoying lights from the audience.
To be honest even if you're not a huge Abba fan I think you'd enjoy it for the technology and the experience!