Well the biggest difference was obviously race, Roman slaves were taken from all corners of the empire so you would have slaves of all races from Celtic and Germanic tribes to Africans. Out side of this slavery is slavery, a better comparison is with Greek and Roman slavery. Slaves in ancient Greece had more personal relationships with their masters often working alongside them in their trade and while this did happen in Rome many many more slaves were used on mass in public works and construction also. Romans tended to have more brutal treatment of slaves while Greek slaves tended to be treated better relatively however Greek slaves were often passed down to family members as assets whereas Romans quite often but not all ways would free their slaves especially after great service or upon their deathbeds. So while treatment was more brutal, you tended to have a better chance of gaining your freedom in Rome.

A number of laws were eventually brought in to protect slaves in Rome so in this sense Roman slaves had it better than American ones. Roman slaves who were able to birth a certain number of children were given their freedom as the master had made up his numbers. Laws were brought into effect which stated Masters could not kill slaves without valid reason where as in America this was not the case. Hope I have been helpful.