It's great - if you like big cities! (7)
I believe the answer is:
capital
'it's great' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for capital that I've seen before include "What starts this clue" , "Hamilton, perhaps" , "Finance - excellent!" , "Madrid, say" , "Topping" .)