dd637b1b_Particles_vs__strings__particles
[topic] unification [strings] String theories are essentially unique in their critical dimension, and unify all forces and particles, including gravity. But "compactification" to D=4 is far from unique, and destroys any advantages of unification. [particles] 
Predictabilty strongly restricts the class of allowed models, but there is still a lot of freedom. Observed matter (quarks and leptons) can be unified, resulting in a unification of forces (less gravity, plus yet unseen forces), but requiring many yet unseen and un-unified "Higgs scalars" to break the symmetry. Supersymmetry introduces unseen particles as least as numerous as the known ones, and thus is not truly unifying.
Particles vs. strings
particles