What is it about?
The hologram concert is a pre-recorded performance of several songs by each of the artists, which is somewhere between a really fancy concert stage and an MV. It has a certain 3D effect, too. When you come to the venue, you will see paper cut-outs of the groups (mainly Big Bang), a souvenir shop, two photo booths where you can take photos with the holograms, some displays related to the idols and their MVs and three screens where you can take pictures while posing together with the singers. You should be also able to dance along the MV being shown on a big screen on a special pad but it didn't really work when we were there. Before the concert starts, there will be a couple background dancers and other entertainers brightening up the mood. The concert itself is shown inside a small hall with 3 walls acting as projection displays. You can stand or sit, though the staff encourages everybody to stand, dance a bit and have fun. Before the actual performace happens, you will take a funny photo of your face in a special photo booth (by all means do it, because then you will become part of the hologram performance and you can also win a free photo) and there will be some background dancers too. Afterwards the three artists/groups "perform" - several songs, a short speech (Korean with English subtitles) and a competition. I won the PSY competition. =D
For cheaper tickets, try to get a double ticket for this and some exhibition in Dongdaemun, if there's anything interesting - it will save you about 40% of the total fees. Otherwise buy the ticket online, or if buying in person, at least get the 10% discount leaflet from the Global Tourism Center. Do not expect to be able to shop after the last concert is over - they close the souvenir store early, so shop before, if you booked the last slot of the day. You cannot take photos inside the concert hall but everywhere else it's fine.
Big screen with MVs