Having only watched Andromeda and the odd episode of Hercules, I have to say, he can act. This is rare in a guy with brawn, but Andromeda cast three actors with both muscle and acting talent. (The guys who player Tyr Anasazi and Telemachus Rhade being the other two). Unfortunately, there was a noticeable shift when Mr. Sorbo became more influential over the direction of the show. It seemed like less of an epic and more like Hercules - Sorbo beating people up and being an all round stock character. In fact, most of the characters turn from 3D to 2D. This is because Sorbo's influence made Robert Hewitt Wolfe, the original developer, leave the show, and it suffers greatly.
In summary, from what I've seen with Andromeda, Mr. Sorbo is an excellent actor, which is a strength he should stick with. He limited himself by influencing the direction of Andromeda rather than acting well, which could've made it as big as other big Sci-Fi shows.