Cardiff isn't a crowded city. Our city centre is tiny by most standards and to have the castle and the parks behind it a stone's throw away is a big thing. Plenty of open space. More could be done with the lawns outside of city hall and the museum but there's Gorsedd Gardens in the middle of the civic centre.
If they'd planned Callaghan Square properly and built an actual square with buildings around it instead of a bloody dual carriageway between the north and as yet undeveloped southern end we could have used that. Arguably we still could if the Welsh Assembly and the Council wanted to.
As far as Central Square is concerned I like the plan as it is, nice and dense with a little bit of space between the outside of Central Station and the new BBC offices.
EDIT : If you look at the amount of space in the image below between Central Station, the new bus station development and the BBC offices it's not bad, hardly too packed in.
