One of the biggest problems with SC2013 was the fact it was called SimCity, they should have tried to make it into its own separate game that focused on small town plots and the regional interactions between them. The building tiles were just far too small to be taken seriously and the 'cities' (if you can call them that!) were always crippled by having a single point of entry in.
That said as flawed as SC2013 was, it did have a few great ideas in there. I loved the city specialisations, making mining, drilling towns and then having to rebuild as the resources ran out in favour of more environmentally sound tourist towns gave the towns a sense of progression, a story if you will. Don't get me wrong I know a lot of the agent systems behind those specialisations were broken (particularly gambling and
nightrush casino) as Costarring points out however if they had worked and the many others flaws were ironed out I honestly think they would have been fantastic. The modular buildings were also a great idea, the way you could add more generators to power stations, more fire engines to the fire station and different schools to the university etc. With Skylines you just plop service buildings down and call it a day, it has less in terms of gameplay than SimCity 4 in a lot of ways because it lacks anything similar to regions and the resource sharing that comes with it. My other issue with Skylines are the completely bland looking buildings that progressively become worse as they upgrade (the futuristic looking skylines buildings are truly terrible looking). I also miss the little maxis quirks that were in SimCity games, silly things like clicking on a police kiosk and hearing snoring hehe.
With that said I will admit that CSL does a lot of things right, the option for huge maps are a must for a city builder and the way public transport is setup and works is fantastic and leagues ahead of any SimCity game to date. I suppose my perfect city builder game would be a mixture of the regional elements of SimCity4, the modular and specialisation bits of SimCity2013 with the scale and mass transit of CSL! Sadly that game will likely never exist, but if it did, I'd never leave my house [haha].