"Built" refers to anything man made, from street lighting to buildings to roads to pedestrian walkways to bridges to paving to quay walls.
"Unbuilt" refers to everything else, including the historical context that Griff refers to, as well as the renewal of several areas in the City including the Courthouse, Rosbrien Road, Steamboat Quay, etc.
There is a tension in architecture at the moment, as the whole axis of design turns from "in your face style" commercialism to the green "help your planet go carbon neutral" agenda and you might find some examples of both in Limerick.
I don't think they're looking for a pat answer or a history lesson. They want your appreciation of your environment. I don't think you should limit yourself by reading architectural polemics and parroting them back to the assessors - it will sound false to them.
If after you've given your honest opinion, whatever it may be - you make some references to work you like - well and good.
You could relate the good and bad here to your previous experience in your own country, for example the public buildings in the neo-classical mode in Eastern Europe under communism, viewed in contrast to Murray O'Laoire's more free-form modernist work.
It really depends on you and your own views and if you have strong views you should express them as best you can, perhaps even including concept sketches to illustrate your central points.
This about how architecture appeals to you, but don't get too wound up about it.
A strongly themed portfolio showing some design maturity and understanding of buildings will mean a lot to them and I would include some analytical studies or sketches in it.
This the appreciation of the building in context, the urban form the positive of the buildings forms, the negative of the spaces between them and how the buildings form these spaces.
The way some buildings make exterior rooms while others glory in themselves, whether Blob or Prism architecture or Meccano architecture [my terms BTW, one borrowed].
The fact that in this century for the first time, more of us will live in cities than outside them may open a discussion about Urban Landscaping as opposed to Urban Planning, vertical gardens and carbon-reducing Titanium cement.
You should probably check out the DOE website and in particular the Ministers statement of intent about how high quality design will shape Ireland in the next few years.
Anyway, whatever you say or write, it should be from the heart and with some feeling.
But that's just me.