Mommsen's text is 150 years old, and it was known to have significant flaws already at the time of publication, notably the unfounded (yet extremely influential) treatment of the Republic as if it were the German federal state. There's no reason to read Mommsen except for historiographical purposes. Even then, Mommsen is usually only professionally consulted at length for the introductory historiographical survey at the beginning of books and dissertations (and usually never brought up again), or sometimes if a publication is dealing with a point from his Staatsrecht, which has withstood the evolution of the field better than the Geschichte. Most ancient historians don't even bother to read Mommsen anymore, at least not in full, in no small part because Syme took down Mommsen pretty thoroughly. And we've mostly moved on past Syme at this point.

There are better options, as well as surveys of the imperial world, in the subreddit's book list. I find that the Roman history list is significantly flawed in its scattershot approach, which doesn't have any underlying method or theory behind it, but that's kind of a necessary consequence of the fact that a bunch of different flairs with differing interests put it together independently. What you're looking for is there.