You have to have an admission ticket to Universal to be able to go inside the Citywalk which links both the Islands of Adventure and Universal Studios attractions.
On the other hand, the Citywalk in Universal Hollywood has free access to the public.
There are several shops and restaurants and even a Moviehouse here but it is still quite small compared to Downtown Disney.
There is also a BlueMan Group show in the complex.
If they allow free access to this area after the park closes probably they will have more crowd in the evening.
But even parking in Universal is quite expensive at $15 so I'd rather go to Downtown Disney where parking is free.
