It's a lot bigger than Common Grounds was...and the tables can be pushed back against the walls to make room for dancing. THere's a party every night, different theme each night. The teens have their KTTW card encoded so that they can go to the 10th floor; little brothers and sisters can't get there on the elevator. Of course, others can take elevator to 9 and walk to 10 (the teens don't think of that!).
The new location means a lot less "stray" people just popping in, not realizing what the area is. That was a problem with Common Grounds being right next to the pools.
Teens may choose to participate in the programming or choose to just "hang out." This is a big change from the Lab, where if you are checked in, you are expected to participate.