The TPP is about something-or-other. Hard to say what exactly that may be, as it's all secret!
The leaks reveal that it's largely about eliminating tarrifs and streamlining customs procedures between members to reduce the cost of international trade. There is also some meddling in domestic politics (It restricts the size of state-owned enterprises, part of the US's long battle against the evil commies). The contriversial parts are the intellectual property reforms. These involve shifting much of the burden of enforcement onto ISPs - requiring they block infringing websites without all that hassle of a court order, or else become liable for the infringement themselves. It appears to also broaden the scope that can be covered by patents (I'm not sure if it actually requires members recognise software patents, most of the concern is about drugs) and prohibits members from passing crisis-exemptions to allow manufacture of cheap generic drugs in the event of a public health crisis.
A lot of it is likely to duplicate the SOPA law that didn't pass in the US. Thus the secrecy. There was enough public outrage against SOPA to defeat it, so this time the backers have learned from the experience and will make sure the content of the treaty doesn't become publicly known until *after* it's been ratified. The public cannot be outraged about that they do not know about.
The Worker's Rights issue, I think - I'm not at all sure about this - relates to TPP making it a lot less risky and a lot cheaper to outsource internationally. It doesn't directly lower standards, but rather could trigger an international 'race to the bottom' to bring wages down. Good for the manufacturers and consumers, but not good for the employees, who will see even more of their jobs disappear and relocate to Vietnam where wages are even cheaper than China, unions are illegal and health-and-safely law is a distant dream. Currently outsourcing is limited by the expense of customs, tarrifs, shipping and regulation. TPP does away with a lot of that, and allows companies to very easily simply shift their operations to wherever the costs are lowest - which means whichever country has the least worker protection is going to attract industry to exploit that, and the only way to retain jobs is do do away with things like unions and workers' rights that make places like Vietnam look so attractive in comparison to employers.