It's pretty cool. The first floor is all manga and toys/collectibles, the 2nd floor has games, movies, CDs, and trading cards, and I haven't gone to the higher floors as they have mostly anime/porn stuff I'm not interested in. They don't have the biggest selection or best prices in terms of games, but I always seem to find something amazing.
The one in Umeda is pretty cool too, but they keep 90% of the boxed retro games behind the check-out counter. It's annoying.
I didn't know there was one in Den Den Town! Where is/was it??