I am not aware of any limitation of nsubstitute
Few years ago I was an adept of moq, and now I have a preference for nsubstitute. I like the syntax (you call directly the method vs setup.), I think NSubstitute has the best syntax and is the most readable of all the frameworks (but this is a subjective assertion ^^).
Oh maybe one thing : NSubstitute don’t have a strict mock mode (but I always thought it was a bad idea, so I never saw it as a limitation)