The concept of The City and The Stars is interesting, the characterisation is weaker than many of Clarke's other novels but it doesn't detract too greatly from the quality of the story. A city who's inhabitants do not venture outside of its walls, one where they choose to live and can decide to go back into the 'banks' ready to come back much later in the city's existence is intriguing.
It is however not clear, at least to me, what exactly the inhabitants do all day, but we know that one resident, Alvin, is unhappy with his existence and wants to explore outside the city walls. I find it strange, that this most innate human desire, to explore, is almost completely absent from this human society for thousands of years, and this is not explored by Clarke in any great detail, though it is briefly.
When it comes to its end, the prospect of what happens from then on is left undeveloped, and to me that would have been a very interesting exploration to experience.