Every artistic remake of Rome or a specific Roman building always show ancient Rome as a crowded, pristine city of these gorgeous marble structures forming the maze of Rome. However, in these recreations we never see if some buildings were damaged, vandalised, under construction or if the streets have banners for different merchants and rubbish thrown into the gutters, so I wanted to know how realistic these recreations were.
Well, I'd say that although the Romans had a uniquely well structured waste water system, the streets were still far from being clean, especially in the many poor quarters like the Subura. Some of the indicators can be seen e.g. in the remains of Pompeii, were there are stepping stones above street level leading over the street, so one could cross it without having to step on the street. This was most likely to avoid stepping into trickles and puddles when it rained, but it may also indicate that there was quite a lot of filth on street level. Another known fact are the hundreds of graffiti that were found especially in Pompeii, either painted on or carved in house walls, ranging from poetic quotes to puns or obscenities. There are even the remains of board games carved in the floor of the Basilica Iulia in Rome that indicate the ancient Romans did often not exactly treat their urban surroundings with a lot of respect. So I'd say the ancient city of Rome was in a lot of areas far from the clean marble look you might imagine today.
Sources: I don't have any book about Pompeii at hand right now, but the information about its streets and walls is practically everywhere. For information about the Basilica Iulia see: "Giuliani/Verduchi: Basilica Iulia. In: Lexicon Topographicum Urbis Romae. Vol. 1. Rome 1993, pp. 177-179." (in Italian)