Workers and Resources: Soviet Republic. It’s one of the most complex city builders made, and while the interface isn’t great and there are lots of obscure, weird, and downright unintuitive mechanics, it’s so rewarding to play because you can actually construct your infrastructure with materials and time, and so unlike Cities: Skylines or Transport Fever, the game doesn’t become trivially easy when you get a late game map. Those games you can eventually afford massive bridges and tunnels, but that’s not the case in Workers and Resources, because no matter how much money you have, bridges take time to build, and you’ll have to reroute traffic during construction, so you’ll only use them when you really need them.

Also I love the scaling, things like gas stations only require a single truck very occasionally, shall industries require a few trucks, and only the big industries like steel require trains (and only a reasonable amount too). As opposed to Cities: Skylines or Transport Fever where every industry ends up with a massive number or trucks or a silly number of trains.