Maybe it's unclear what this modcomp does. We may want to skip it and eventually (2011) build a city-examination screen instead, but that's orthogonal to this question.
When you capture a city, you are presented with an immediate popup asking if you want to keep, raze, or (sometimes) return it to its previous owner. At this point in the code, the city has already been recreated attached to your player, and whatever buildings remain you'll get if you keep it. The modcomp adds a "Examine the city" button which opens the city screen for that city.
You will see the buildings that survived the conquest and the settled great people. These two are the pieces I consider unaltered. Plus you can see everything else: trade routes, food, production, commerce, maintenance, etc, but that's more an effect of the buildings, great people and population, and it won't be meaningful until the city gets out of revolt anyway--after you've already decided to keep it.
How is this unaltered?
1. It's hard to tell what buildings survive the conquest of the city given that the unit that took it is standing on the city itself. Sure, you can turn on Bare Map View before the unit takes the city, but I don't know if the graphics are updated or not (they probably are).
2. You can see the settled great people. Without EP points to be able to investigate the city, you can't see these normally.
Maybe this is a feature for BUG-FE.