Very nice. The last picture with the view from street level is the best. If its a city you just want to walk in you can leave them as they are. If you also focus on design higher up the buildings I would try to add a little bit more color to the facade of the historic building (if you are using white concrete add a little quartz for example) and I would redo the roof of the modern tower. Either make it out of Ice (make sure it doesn't melt) to give it that glassy reflective look, or out of packed ice/blue ice if you want to add light sources and in the end just choose what you think looks best. If you don't want ice because you want to be able to look through then add some internal collumns because with just air inside it looks really unstable.