For the past seven months, I've been designing, building, and theming with Drupal 8 for my own side project. Along the way, I've seen huge advancements in these realms versus what was possible with Drupal 7.
In Drupal 8, there's templates for just about anything and with Drupal 8's new theme hooks, you can really narrow in on crafting a custom template for your specific use case. This makes getting at and altering markup far more accessible than it was in Drupal 6 and 7.
My uncle used to say, "You have to use the right tool for the job." This is no different when it comes to Drupal 8 theming and development.
Now that I'm digging into Drupal 8 theming and its awesomeness, I'm discovering some really useful methods and functions. At the same time, I'm learning a lot and having fun.