It's essentially Harvest Moon 2.0. Everything that was great about the 8 / 16-bit era games returns, only much, much more fleshed out. There is level progression for each of the skills (farming, mining, fishing etc) which really adds to the sense of progression. Minecraft style crafting of materials is also a great way to expand the tools at your disposal.
The best part is though, you are completely free to do what you want, without heavy financial penalty, so if you want to fish all day and neglect the farm, you can do it. You can explore the caves, expand your farm, improve the town, find artefacts for the museum or work on relationships with the inhabitants for rewards, you can focus on one or more of these aspects and still find a deep and interesting game.