Jim W.
Yelp
This is actually spread out over 2 (or more) buildings. These are diagonally across a large intersection from each other. Both are across streets from the Termini (train) Station. Also - our city pass purported to include this place for admission. However, when we arrived they said that there had been some change and it was not covered. We paid their fee anyway. Later, we got a reimbursement from the city pass company for this.
We began our tour in the building to the right when you are facing the train station. It houses mostly statuary from the period from Julius Ceasar forward. They have busts of many of the emperors from the first couple of centuries of the empire (and their families, in some cases). There are other statues as well, plus things like a huge room's preserved wall paintings that were unearthed nearby. It is definitely heavy on busts, but I thought it was interesting.
We then crossed the streets to the 2nd building, which is incorporated into the remains of a vast Roman baths complex. They had a variety of different exhibits here - about the baths, some more sculptures, an odd small shrine that was unearthed during a construction project (and which was preserved in a parking garage), details about pre-Roman villages in the area, etc. You could browse through and focus on a few areas of interest. There were also multiple courtyards to examine, each with its own statuary.
This set of museums is probably best viewed after touring things like the Forum or Colosseum first. You then may have some basic context of where things happened, and can then start adding details about the major figures associated with the time period (and get some idea of what they looked like too). I enjoyed spending a morning here.