Be aware that it is absolutely freezing in winter though, -40C ...
Most people prefer Almaty, the old capital, more cosmopolitan, a more tolerant and laid back city ... Astana is ummm, do you know the term "Potemkin village"? ...
It is blingy and weird, pretty much for show and as a place to keep the bureaucrats and politicians and attempt to impress politicians and business people from other countries ... it is really only 14-15 years old, perhaps it will grow into something one day ...
If you are coming for the nightlife ... hmmm, there would perhaps be better places and countries to consider ...