I'm sure you have to pay to enter because there would be no way to keep track of "observers." You can come and go- may need a hand stamp or something.
We took DD6 and DS4 for the first time in February. We all really enjoyed the Pirates and the Jungle Cruise attractions. We didn't do any of the virtual reality attractions that require you wear a helmet because DS would have no part of that! We played TONS of "free" 80s video games and the kids played lots of skeeball, air hockey, etc. They called it Disney Chuck E. Cheese and loved every minute of it.
My family isn't particularly into video games. My kids were also too young for many of the major attractions. We had free upgrades on our tickets so going was worth it. I would have a really hard time actually paying because for us it WAS a Chuck E. Cheese experience (other than Pirates and Jungle Cruise.) I think we spent ~ 3 hours there.
I imagine kids (or adults) who are really into video games would love this place more than the parks! Teens and Tweens could probably spend multiple days here. It's fun, but not really worth the $$$ if your kids are too young for all the major stuff.