Mixed/Neutral
Massive Freedom Fighter for his work in organizing the unorganized into democratic labor unions, but I have a highly negative opinion of his purging political opponents within the CPUSA and his support for Stalin (which is forgivable, I think up to a point because of how little people knew about what was actually going on in the USSR during his tenure, but not on his account because Foster knew exactly what was going on and continued to support Stalin and the USSR after its crushing of socialist revolutionaries in Hungary).
Towards a Soviet America is an excellent read, however, and I would encourage everyone with an ounce of interest in what a socialist America might look like to check into it. He was also a strong supporter of civil rights (unlike the mainstream leadership of the United States at the time) and so that gives him obvious FF points too. But all in all a mixed figure.