Shen's taunt is versatile and you can get creative with it. It's also mobility, meaning it has multiple uses. Additionally, his taunt is not telegraphed like Galio's and can be used to engage unlike Rammus'. Galio is slowed and Rammus has to stop and go through the cast lock-out period (yes, there is one). Additionally the way it can be used can be crazy (taunt-flash) while Rammus/Galio can only do one or two tricks with their taunts.
Additionally, it scales in damage with his HP and his W is a pseudo-secondary effect in a combo of E-Q-W in which he blocks all autos for a brief period.
I have many complaints about Shen's current state from his counter-intuitive ult scaling to the inferiority of his only damage tool on Q to Cho'gath's throwaway ability on E. However, Shen's taunt IMO is fine and with any more power put into it he would become a bit one-directional (Basically it would become a fact that if you don't land taunt you're useless, for example).
Hopefully that answers your question.