Your question is hard to answer without really knowing more. I mean what does "poorly" finished exactly mean. However, you shouldn't plaster it. If it's really that bad, I would cut out the bad section and replace it with new drywall.
The drywall joints are kinda rough. You can easily see the joints. With a lot of work, it could be fixed with joint compound. However I dislike drywall and would prefer the much harder and more durable surface of veneer plaster. In my experience, it is actually easier to smooth-out bad joints with plaster too. If I can simply apply a paint to the existing drywall and then plaster it, then that would be better than completely ripping out the drywall and replacing it with blue board/veneer plaster.