Good' and 'bad' are value judgements applied to things relative to how well they meet our expectations.
Taoism has no equivalent form of assessment. It gauges value relative to whether or not something is true to its nature.
In terms of tai chi, there is no such thing as good or bad tai chi. There is tai chi, and there is exercise or martial arts practice that simply cannot be called tai chi.
Tai chi follows certain taoist principles and must meet certain criteria. It is a martial art, a viable, working form of self defence. It uses softness and yielding rather than force and aggression.
It is also a way of moving, a way of interacting and a way of being.