For me, other than the obvious size difference, the difference between microservices and "large" (?) services is that a single team breaks down their domain into sensible layers, abstractions etc.
Similarly, A microservices/SOA architecture can fail to break down their domain into good boundaries and abstractions. I've seen this happen a lot.
It's a lot harder to fix bad microservices than to fix a bad monolith
I think certain things are easier to change in a monolith, where as other things are easier to change in a service based design. Depends what mistakes you've made along the way or how the spec/environment changes.